Billing language is where revenue cycle confusion starts. When a practice owner hears that “denials are climbing,” the real problem may be rejections — claims bounced before adjudication — which need a completely different fix. A “collection rate” of 98% can mean very different things depending on what sits in its denominator. Medical Billing Services Group (MBSG) maintains this glossary as a plain-language reference for the terms that drive revenue cycle decisions — written for practice owners, managers, and billers, not just coding specialists.

How to use it: each entry stands alone, so start with the term you need. Definitions use plain US English and add practical context — what the term means, why it matters to cash flow, and where it sits in the revenue cycle, from eligibility and prior authorization through claim submission, denial management, and collections. Where a topic deserves deeper coverage, entries link to the relevant page, such as our revenue cycle management overview or our services page.

Two notes on how these definitions are written. First, they are educational and general: requirements vary by payer, plan, setting, and date of service. Medicare rules do not always match a commercial payer’s, and both change. Always verify against the payer’s current published policy and, for coding questions, the authoritative source — for example, the CMS National Correct Coding Initiative (NCCI) policy manual (https://www.cms.gov/medicare/coding-billing/national-correct-coding-initiative-ncci-edits/medicare-ncci-policy-manual) or the CMS place-of-service code sets (https://www.cms.gov/medicare/coding-billing/place-of-service-codes/code-sets). Where an entry cites an official source, the note sits beside the claim. This glossary was last reviewed on 2026-10-07.

Second, terminology evolves, so this is a living reference: new entries are added as the set grows, and definitions are re-checked on review. What it covers today: the claim lifecycle (clean claims, rejections, denials), the money metrics (A/R days, net collection rate, contractual adjustments), the front-end gateways (eligibility verification, prior authorization, payer enrollment), and the plumbing that moves data and dollars (clearinghouses, ERA and EOB).

General educational information, not legal advice or a guarantee of reimbursement. CPT is a registered trademark of the American Medical Association.

Starter entries

Clean Claim

A clean claim is a claim submitted to a payer with all required information complete and accurate — correct patient demographics, valid diagnosis and procedure codes, the right place-of-service code (CMS place-of-service code sets: https://www.cms.gov/medicare/coding-billing/place-of-service-codes/code-sets), and filing within the payer’s timely-filing deadline — so it can be processed without manual intervention. Clean claims matter because they move straight to adjudication: every claim that fails an edit and comes back for correction costs staff time and delays payment. Practices track the clean claim rate (clean claims divided by total claims submitted) as a front-end quality metric. Common reasons claims are not clean include missing or invalid diagnosis codes, mismatched patient information, services bundled incorrectly under NCCI edits (CMS NCCI policy manual: https://www.cms.gov/medicare/coding-billing/national-correct-coding-initiative-ncci-edits/medicare-ncci-policy-manual), and filing past the timely-filing limit. A high volume of unclean claims usually points to registration, coding, or scrubber problems upstream — which is exactly what an outsourced medical billing review or a billing audit is designed to find.

Claim Rejection vs Denial

These two words describe failures at different stages, and mixing them up leads to the wrong fix. A rejection happens before adjudication: the clearinghouse or the payer’s front-end system refuses to accept the claim because of a formatting or data error — a missing field, an invalid code, a patient not found. A rejected claim was never processed, so it is corrected and resubmitted, not appealed. A denial happens after adjudication: the payer processed the claim and decided not to pay — for example, for lack of medical necessity, a bundling edit, or missing prior authorization. Denials require appeals, corrected claims, or write-off decisions depending on the reason code. Tracking rejections and denials separately matters: rising rejections point to front-end data quality, while rising denials point to payer policy, documentation, or authorization problems. Learn how structured follow-up works on our denial management page.

A/R Days (Accounts Receivable Days)

Accounts receivable (A/R) days measures how long, on average, it takes a practice to collect on billed charges. The formula: total outstanding A/R divided by average daily charges, where average daily charges equals total gross charges over a period divided by the number of days in that period. For example, $300,000 in outstanding A/R with average daily charges of $10,000 equals 30 A/R days. The metric compresses the entire revenue cycle — registration accuracy, claim submission speed, payer turnaround, denial follow-up, and patient collections — into one number. Rising A/R days signal that money is stuck somewhere: unworked denials, slow payer processing, or patient balances aging without follow-up. Because it blends everything, A/R days works best alongside its component metrics rather than alone. Practices struggling with aging receivables often start by reviewing their collections workflows.

Net Collection Rate

Net collection rate answers a sharper question than gross collections: of the money the practice was actually allowed to keep, how much did it collect? The formula: total collections divided by (gross charges minus contractual adjustments) — that is, net collectible revenue. Excluding contractual adjustments from the denominator is the point: a payer contract that reduces a $200 charge to a $120 allowed amount is not a billing failure, so the $80 contractual adjustment should not count against the collection rate. A rate near 100% suggests the practice collects nearly everything payers and patients owe; a falling rate suggests denials going unworked, underpayments, or patient balances written off without effort. Pair it with A/R days and denial rates to see both how much and how fast revenue is captured. Requirements vary by payer, plan, setting and date of service.

ERA and EOB

The electronic remittance advice (ERA) and the explanation of benefits (EOB) are how payers report what happened to a claim. The ERA is the electronic version, delivered through the clearinghouse or payer portal in a standard format, and it is what billing software auto-posts: payment amounts, adjustment reason codes, and denial codes for each claim line. The EOB is the patient-facing equivalent, typically a mailed or portal document showing what was billed, what the plan paid, and what the patient may owe. Both use the same vocabulary — allowed amounts, deductibles, copays, and procedure (CPT) codes. Fast, accurate ERA posting is the backbone of denial follow-up: reason codes on the ERA tell the billing team exactly which claims need appeals, corrections, or patient billing. Delayed or unposted remittances are a common hidden cause of inflated A/R. CPT is a registered trademark of the American Medical Association.

Payer Enrollment

Payer enrollment is the process of getting a provider — and the practice’s group — approved to bill each insurance payer and receive payment. It includes credentialing (verifying education, licensure, and history), submitting enrollment applications such as Medicare’s PECOS or commercial payer forms, obtaining NPIs and taxonomy codes, and linking providers to the practice’s tax ID and payment address. Enrollment is slow: applications can take weeks to months, and a provider who sees patients before enrollment is effective may generate claims the payer will not pay. Common failure points include expired licenses, mismatched addresses, and revalidation deadlines missed years after the initial approval. Because each payer has its own forms, portals, and timelines, practices with multiple providers often treat enrollment as a continuous administrative function rather than a one-time task. See our credentialing and payer enrollment services.

Prior Authorization

Prior authorization is a payer’s requirement that certain services be approved before they are provided. The practice submits clinical documentation — diagnosis, planned procedure, and medical necessity support — and the payer approves, denies, or requests more information. Authorization is not a payment guarantee: an approved authorization can still result in non-payment if eligibility changed, the claim was coded incorrectly, the service fell outside the authorized window, or medical necessity documentation was insufficient at claim review. Prior authorization delays are a leading cause of denials and rescheduled care, so practices track authorization turnaround alongside denial rates. Requirements vary widely by payer, plan, setting and date of service — what needs authorization for one plan may not for another. Front-end eligibility and prior authorization workflows exist to catch these requirements before the visit, not after the denial.

Eligibility Verification

Eligibility verification is the front-end check that a patient’s insurance is active and covers the planned service on the date of service. It confirms the payer, plan, effective dates, copay and deductible status, referral or authorization requirements, and whether the provider is in network. Verification happens before the visit — ideally at scheduling and again at check-in — because nearly every downstream billing problem is cheaper to prevent here: inactive coverage, out-of-network status, and unmet deductibles discovered after the visit become denials, write-offs, or surprise bills. Many practices automate verification through their clearinghouse or practice management system and reserve manual checks for complex cases. Accurate eligibility data is also what makes cost estimates and point-of-service collections possible. It pairs naturally with prior authorization in the eligibility and prior authorization workflow.

Clearinghouse

A clearinghouse is the intermediary that moves claims between a practice and its payers. It receives claims from the practice management system, scrubs them against payer-specific edits, and routes accepted claims to the correct payer — then returns rejections, ERAs, and status updates the other way. Its role is connectivity and editing, not ownership: the clearinghouse does not adjudicate claims, set payment policy, or decide medical necessity; the payer does. Clearinghouses also typically provide eligibility checks, claim status inquiries, and ERA delivery, which makes them central to daily billing operations. Limits to understand: a claim that passes clearinghouse scrubbing can still be denied by the payer, and clearinghouse edit rules do not replace payer policy research. Practices evaluate clearinghouses on edit quality, payer connectivity, and how clearly rejections are explained. See clearinghouse services.

Contractual Adjustment / Write-Off

A contractual adjustment is the difference between what a practice bills and what a contracted payer allows — written off as a condition of the payer contract. If the billed charge is $200 and the payer’s allowed amount is $120, the $80 difference is a contractual adjustment, not a loss to chase. Write-off is the accounting action of removing that amount from receivables. Contractual adjustments must be distinguished from bad debt (patient balances deemed uncollectible) and from administrative write-offs (small balances or timely-filing write-offs). Inflated or miscategorized adjustments distort the net collection rate, which is why the metric excludes them from its denominator. Reviewing adjustment patterns by payer can also surface underpayment: if the allowed amount applied does not match the contract, the difference may be recoverable. Underpayment recovery is part of disciplined collections follow-up.

Frequently asked questions

Is this glossary legal or billing advice?

No. These entries are general educational information, not legal advice or a guarantee of reimbursement. Requirements vary by payer, plan, setting and date of service — always confirm with the payer’s current published policy.

Do these definitions apply to every payer?

They describe how the terms are generally used in US medical billing. Individual payers may define processes, deadlines, and documentation requirements differently, and policies change. The payer’s manual governs adjudication.

How current is this glossary?

This page was last reviewed on 2026-10-07. Billing rules change, so treat entries as a starting reference and verify time-sensitive details against current payer guidance.

Can I share these definitions with my team?

Yes — the glossary is written to double as an internal training aid. If you republish entries elsewhere, link back to this page as the source.

What if a term here conflicts with my payer’s manual?

Follow the payer’s manual. Payer-published policy controls how your claims are adjudicated and paid.

Will new terms be added?

Yes. New entries are added as the reference grows, using the same plain-language standard and source notes.