401K

A 401(k) plan is a qualified retirement plan established by an employer (business) for its employees. Under a 401(k) plan, eligible employees may defer a portion of their wages/salary to their account under the plan. These deferred amounts are referred to as salary-deferral contributions, and can be made on a pre-tax and/or post-tax basis. Earnings in a 401(k) account grow on a tax-deferred basis and distributions are treated as ordinary income when distributed from the account. 

(Source: Retirement Dictionary)