A 401(k) is a retirement savings plan offered by many employers that allows employees to save a portion of their paycheck before taxes are taken out. This means that the money you contribute can grow tax-deferred until you withdraw it in retirement. Many employers also offer matching contributions, which can help boost your savings even more. Participants can choose how to invest their contributions, typically in a range of options like mutual funds or stocks. There are limits on how much you can contribute each year, and early withdrawals may incur penalties. Overall, a 401(k) is a valuable tool for building retirement savings.