What is 401(k)?
A 401(k) is an employer-sponsored retirement account in the United States. You contribute from your paycheck, often before income tax, the money is invested in the funds your plan offers, and some employers add matching contributions.
Why it matters
Matching contributions are effectively part of your pay, and automatic payroll deductions make it an easy way to invest steadily. Contribution limits and withdrawal rules are set by law and change over time, so check current rules.