It’s the technical term for the money you transfer from a 401(k) to another retirement account, like an IRA. It’s what most people choose to do with the money they’ve saved in their 401(k) account when leaving a job. A rollover is different from a withdrawal, which is when you pull your money out of a 401(k) and pay taxes on it. A rollover is tax-free because your money stays in a retirement account.