- Annual Enrollment Period (AEP)
- October 15 to December 7 each year. Anyone with Medicare can join, switch, or drop a Medicare Advantage or Part D plan. Changes start January 1.
- Annual Notice of Change (ANOC)
- A letter your Medicare Advantage or Part D plan must send by September 30 listing every change to your plan for the coming year.
- Coinsurance
- A percentage of the cost you pay for a covered service after any deductible, such as 20%.
- Copayment
- A fixed dollar amount you pay for a covered service, such as a set amount for a doctor visit.
- Creditable coverage
- Drug coverage expected to pay, on average, at least as much as standard Part D. Having it lets you delay Part D without a late penalty. Your employer or union plan sends a yearly notice saying whether it qualifies.
- Deductible
- The amount you pay for covered services before your coverage starts paying.
- Extra Help
- A Medicare program that helps people with limited income and resources pay Part D premiums, deductibles, and copays. You apply through Social Security.
- Formulary
- A plan's list of covered prescription drugs, usually grouped into tiers with different costs.
- General Enrollment Period
- January 1 to March 31 each year, for people who missed their Initial Enrollment Period to sign up for Part B. Coverage starts the month after you sign up, and a late penalty may apply.
- Guaranteed issue right
- A situation where a Medigap company must sell you certain policies without using your health to turn you down or charge you more.
- HICAP
- California's Health Insurance Counseling and Advocacy Program. It is California's State Health Insurance Program and offers free, unbiased Medicare counseling at 1-800-434-0222.
- HMO
- Health Maintenance Organization. A type of Medicare Advantage plan that generally requires you to use in-network providers and get referrals for specialists, except in emergencies.
- Initial Enrollment Period (IEP)
- Your first chance to sign up for Medicare: 7 months, starting 3 months before the month you turn 65 and ending 3 months after it.
- IRMAA
- Income-Related Monthly Adjustment Amount. An extra amount added to Part B and Part D premiums for people whose income is above certain levels, based on tax returns from two years earlier.
- Late enrollment penalty
- An amount added to your Part B or Part D premium if you did not sign up when first eligible and did not have qualifying coverage. It usually lasts as long as you have that coverage.
- Maximum out-of-pocket limit
- The most you pay in a year for covered Part A and Part B services in a Medicare Advantage plan. After you reach it, the plan pays 100% of covered services for the rest of the year.
- Medi-Cal
- California's Medicaid program. People who have both Medicare and Medi-Cal are often called dual eligible and may qualify for special plans and extra cost help.
- Medicare Advantage (Part C)
- A private plan approved by Medicare that provides your Part A and Part B benefits, usually through a provider network. Most include Part D drug coverage.
- Medicare Advantage Open Enrollment Period
- January 1 to March 31. If you are in a Medicare Advantage plan, you can switch to another Advantage plan or return to Original Medicare and join a Part D plan, one time.
- Medicare Part A
- Hospital insurance. Covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. Most people pay no premium for Part A.
- Medicare Part B
- Medical insurance. Covers doctor visits, outpatient care, preventive services, lab tests, and medical equipment. Most people pay a monthly premium.
- Medicare Part D
- Prescription drug coverage offered by private plans approved by Medicare, either stand-alone or within a Medicare Advantage plan.
- Medicare Prescription Payment Plan
- An option through your drug plan that lets you pay your out-of-pocket drug costs in monthly amounts across the year instead of all at once.
- Medicare Supplement (Medigap)
- A private insurance policy that helps pay costs Original Medicare does not, such as deductibles and coinsurance. Plans are standardized by letter and only work with Original Medicare.
- Medigap birthday rule (California)
- A California protection: if you have a Medigap policy, you get a 60-day window each year starting on your birthday to switch to another Medigap policy with the same or fewer benefits without medical underwriting.
- Medigap Open Enrollment Period
- A 6-month period starting the first month you have Part B and are 65 or older. During it, a company cannot use your health to deny you a Medigap policy or charge you more.
- Network
- The doctors, hospitals, pharmacies, and other providers a plan contracts with to provide care.
- Original Medicare
- Part A and Part B, managed by the federal government. You can see any provider in the U.S. that accepts Medicare.
- PPO
- Preferred Provider Organization. A type of Medicare Advantage plan with a network, where you can also see out-of-network providers, usually at higher cost.
- Prior authorization
- Approval a plan requires before it covers a specific service or drug.
- Scope of Appointment
- A form that records which types of Medicare plans you agreed to discuss with an agent before a sales meeting. It protects you from being pitched products you did not ask about.
- Special Enrollment Period (SEP)
- A window outside the usual dates to change coverage, triggered by events like moving, losing other coverage, or qualifying for Extra Help or Medi-Cal.
- Star Ratings
- Medicare's 1 to 5 star quality ratings for Medicare Advantage and Part D plans, published each fall on Medicare.gov.
- TPMO
- Third-Party Marketing Organization. Agents, agencies, and other organizations that sell Medicare plans for insurance companies. TPMOs must tell you they do not offer every plan in your area, if that is the case.
- Trial right
- If you join Medicare Advantage when first eligible at 65, or drop Medigap to try Advantage for the first time, you can generally return to Original Medicare and buy Medigap without health questions within the first 12 months.
Where these facts come from: Medicare.gov glossary and program guidance; California Health Benefits Review Program, 2025. Rules and dollar amounts change. Page reviewed October 4, 2026.