Are defined benefits pension plan vested?

It matters what pension system it is. In many public pension systems unless you retire early and take a vested retirement once qualified for, you will not receive benefits if terminated/fired.

A retirement plan, normally a pension, that provides "defined benefits" at a future date, like an annuity. Unlike a defined contribution plan (such as a 401(k)) in which a participant has their own...

BURNS INTERNATIONAL SERVICES CORPORATION RETIREMENT PLAN is a Defined Benefit Plan providing retirees with a predetermined monthly retirement benefit upon reaching a specific age. The retirement...

a set amount an employee will receive at retirement

db plans are pooled asset type plans (both employer and employee $) and expenses are normally deducted/paid from the assets.