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 This means that the money contributed to the account can grow tax-deferred until it is withdrawn during retirement.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