Medicare guidance
Medicare Glossary: Terms and Abbreviations
Look up common Medicare abbreviations and everyday insurance terms, then follow links to the detailed guides that explain the rules.
Quick reference
Common Medicare Abbreviations
ANOC: Annual Notice of Change
The plan’s yearly notice describing changes in coverage, costs or other terms for the coming year. Read it before deciding to keep your plan. Read the detailed guide.
EOB: Explanation of Benefits
A statement describing how a health or drug plan processed care or prescriptions. It is not itself a bill. Compare it with any provider charge. Read the detailed guide.
EOC: Evidence of Coverage
The detailed plan document explaining benefits, member costs, conditions and procedures. Use the document for the correct plan year. Read the detailed guide.
IRMAA: Income-Related Monthly Adjustment Amount
An additional Part B or Part D premium amount based on income. Social Security determines it; it is separate from an insurer’s plan premium. Read the detailed guide.
MOOP: Maximum Out-of-Pocket
A plan’s annual limit on certain covered cost sharing. A Medicare Advantage medical limit does not include every expense, such as all premiums and Part D costs. Read the detailed guide.
MSN: Medicare Summary Notice
Original Medicare’s claims statement showing services billed, Medicare’s decisions and what you may owe. It is not a bill. Read the detailed guide.
MSP: Medicare Savings Program
In assistance-program discussions, a state program that helps eligible people with certain Medicare costs. In billing discussions, MSP can instead mean Medicare Secondary Payer. Context matters. Read the detailed guide.
QMB: Qualified Medicare Beneficiary
A Medicare Savings Program with protection from billing for Medicare-covered deductibles, coinsurance and copayments. It is not the same as having full Medicaid benefits. Read the detailed guide.
SEP: Special Enrollment Period
An enrollment opportunity tied to a qualifying circumstance. Parts A and B, private Medicare plans and Medigap have different rules; there is no universal SEP deadline. Read the detailed guide.
IEP: Initial Enrollment Period
The first enrollment window for a particular Medicare benefit. The ordinary age-65 Part A/Part B window is seven months, with timing exceptions. Read the detailed guide.
D-SNP: Dual Eligible Special Needs Plan
A Medicare Advantage plan for people who meet specified Medicare and Medicaid eligibility conditions. Eligible Medicaid levels and coordination vary by plan. Read the detailed guide.
RRB: Railroad Retirement Board
The federal agency that generally handles Medicare enrollment for railroad retirement beneficiaries. Some situations, including kidney-disease entitlement, are handled through Social Security. Read the detailed guide.
Everyday cost language
Premium, Deductible, Copay and Coinsurance
- Premium
- The amount paid to keep coverage in force, generally monthly, whether or not you use services.
- Deductible
- The amount you pay for applicable covered services before the benefit begins paying under its rules. Not all services use the same deductible.
- Copayment
- A set amount you pay for a covered service or prescription, such as a specified office-visit charge.
- Coinsurance
- A percentage of the applicable covered amount that you pay. It is different from a fixed copayment.
- Assignment
- A provider’s agreement to accept the Medicare-approved amount as payment in full for a covered service, apart from permitted deductible and coinsurance amounts.
For the figures that apply now, use the 2026 costs guide. For payment logistics, see how to pay Medicare premiums.
Plan documents
Network and Prescription Terms
- Network
- The providers, facilities or pharmacies with which a plan has arrangements. Verify the exact plan, location and service.
- Formulary
- A plan’s list of covered prescription drugs, including associated tiers and coverage restrictions.
- Prior authorization
- A requirement to obtain a plan’s approval before it will cover certain services or prescriptions under its rules.
- Creditable drug coverage
- Drug coverage expected to pay, on average, at least as much as standard Medicare drug coverage. Keep the coverage notice when planning Part D enrollment.
Read the Part D comparison guide and provider-network checklist before relying on a label alone.
Use the definition carefully
Similar Names Do Not Mean the Same Benefit
Medicare and Medicaid are separate programs. Medicare Advantage and Medicare Supplement Insurance are different coverage approaches. Extra Help concerns prescription-drug costs; a Medicare Savings Program concerns specified Medicare costs under state-administered rules.
Likewise, a premium bill, an EOB and an MSN serve different purposes. Check the document heading, issuer and coverage dates before deciding that you owe money or need to change plans.
If an abbreviation appears in a sentence that does not fit its definition here, ask the sender what it means in that document. “MSP” is a common example of an abbreviation with more than one Medicare meaning.
Official information
Sources and Further Reading
Sources checked September 10, 2026.
Independent Medicare guidance
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Thompson Medicare Brokerage is not connected with or endorsed by the U.S. government or the federal Medicare program. This educational guide does not replace an official coverage or eligibility determination. Your circumstances and current Medicare and plan rules control.