Bottom line
The Continued Health Care Benefit Program (CHCBP) is a voluntary, premium-based health plan you can buy when you and your family lose your military medical benefits. It is a temporary bridge to civilian coverage that lasts 18 to 36 months. You have to purchase it within 60 days of losing your eligibility, so do not let that window close.
What it means for you
If you are coming off active duty, dropping into the IRR, or otherwise losing your military health coverage, CHCBP keeps you and your family covered while you line up a civilian plan. It is not free and it is not TRICARE, but it gives you TRICARE-comparable coverage for a set stretch of time. The IRR is the main audience for this program, because SMCR and IMA SELRES Marines can usually buy TRS instead at a lower premium. The clock is short: you have 60 days from the loss of your eligibility to sign up.