nonforfeitable
(19) The term “nonforfeitable” when used with respect to a pension benefit or right means a claim obtained by a participant or his beneficiary to that part of an immediate or deferred benefit under a pension plan which arises from the participant’s service, which is unconditional, and which is legally enforceable against the plan. For purposes of this paragraph, a right to an accrued benefit derived from employer contributions shall not be treated as forfeitable merely because the plan contains a provision described in section 1053(a)(3) of this title .