It's a type of life insurance policy that returns most all of the premiums you paid during the term, if you outlive the life of your policy.
So, if you buy a 10 year term life insurance plan with return of premium, and you outlive the ten year term, then you would get back a return of most of the premiums you paid for your life insurance policy.
Keep in mind, the rate you pay for return of premium life insurance is higher than you might pay for regular term life insurance, but if you do live, you get most of the money back.
Learn more about life insurance with premium return.