Indeed, "what are pension funds"? I don't have a pension. No one I know personally has a pensions. The younger or non-tech people I know have little to none in their 401k.
By contrast, a 401(K) is a defined contribution plan. You put however much money in, maybe get matching, and you can take money out after a certain age based on how much you put in and how much it grew.
Defined benefit used to be a lot more common but it's become less so for a variety of reasons including tax law changes. Today you see them mostly in government jobs like teachers.
That seems to be a lot less common now.
https://www.investopedia.com/ask/answers/100314/whats-differ...