What Is A 401(K) Retirement Savings Plan? 
A 401 -LRB- k -RRB- plan is a qualified defined contribution retirement plan under ERISA , the Employee Retirement Income Security Act of 1974 . The pretax contributions accumulate tax deferred and distributions are taxable as ordinary income at retirement . Some employers also match a portion of employee contribution and those over age 50 are allowed additional contributions under the catch up rule . 