"Pensions" in the US generally refer to defined-benefit pensions, i.e. you worked here 10 years with a terminal salary of $100K so you get $X/month starting at age 65 (or whatever).

In general, private sector companies have switched to defined-contribution schemes like 401Ks, which are tied to an employer but can be (and generally should be) rolled over to IRAs when you leave the company.

Social Security is something else again that comes from the government but isn't usually called a pension.