Pension
A pension (defined-benefit plan) is an employer promise to pay you a set monthly amount in retirement, usually based on your salary and years of service. Once common, they've largely been replaced by 401(k)s, which shift the investment risk from the employer to you.
Pensions still exist widely in government and union jobs. If you have one, understand its formula, survivor options, and whether it's inflation-adjusted — and treat it as a guaranteed income layer alongside Social Security when planning the rest of your savings.