A retirement plan, such as a 401(k) plan, an employee annuity plan (26 U.S.C. § 403(a)), an individual retirement account (26 U.S.C. § 408(a)), or a governmental deferred compensation plan (26 U.S.C. § 457), that satisfies requirements of the Internal Revenue Code and is eligible for special tax treatment. For example, generally an employee may defer paying taxes on contributions to a qualified retirement plan until distributions are made.
Rev. Rul. 2007-37 (expanding the list of qualified pension and retirement plans)