A "401k" is a type of retirement savings plan that is offered by many employers in the United States. It allows employees to save and invest a portion of their paycheck before taxes are taken out. This means that the money you contribute can grow over time without being taxed until you withdraw it during retirement. Some employers may also match a portion of your contributions, making it an attractive way to save for the future.
The term "401k" comes from Section 401(k) of the Internal Revenue Code, which governs the plan's tax advantages and regulations.