It goes on line 5a/b of Form 1040 no matter what you call it. TurboTax doesn't ask you to distinguish between a pension and an annuity.
if the there is after-tax basis in the plan, for tax purposes what matters is whether the payment are periodic or nonperiodic. Periodic payments are a proportionate mix of pre-tax and after-tax amounts. Nonperiodic payments consist only of pre-tax amounts until all pre-tax amounts have been distributed; pre-tax amounts are distributed first.
