The insurance policy coverage that is applied first, up to the amount of the loss or the policy limit, when two or more policy coverages apply to the same insured loss. (See also, Pro Rata Other Insurance.)
Insurance that applies to a loss on a first dollar basis. For example, the liability coverage of a homeowners policy is primary insurance. If the insured has a personal umbrella policy, its coverage would apply as excess insurance upon exhaustion of the limits of liability of the homeowners policy.
The insurance organization with first responsibility for paying eligible insurance expenses for your medical service (after you have paid your deductible and co-payments). If you have additional insurance, those organizations would work with your primary insurance organization to cover eligible expenses according to your insurance policies.