Final answer:
In the TRICARE program, a catchment area refers to an area around a U.S. military treatment facility that is defined by ZIP codes and serves as the basis for determining eligibility for care and services.
Step-by-step explanation:
In the TRICARE program, an area, defined by ZIP codes, that is approximately 40 miles in radius surrounding each U.S. military treatment facility is called a Catchment Area. This catchment area helps determine which beneficiaries are eligible to receive care and services at a specific military treatment facility. It ensures that the facility can effectively provide healthcare services to its assigned population.