noun
retirement savings; savings for old age
Refers to money saved specifically for living expenses after retirement.
老後資金を貯めるために、毎月少しずつ積み立てている。
I'm putting aside a little each month to build up my retirement savings.
年金 is a pension or annuity, often a regular payment from a system, while 老後資金 is the broader pool of savings for old age.
Compound of 老後 (old age) and 資金 (funds, capital).