What do the following actuarial terms mean: accumulated benefits, actuarial liability, vested benefits, service cost, and unfunded

Question:

What do the following actuarial terms mean: accumulated benefits, actuarial liability, vested benefits, service cost, and unfunded accumulated benefits? How are they measured? How are projected benefit obligations, accumulated benefit obligations, and vested benefit obligations defined in SFAS No. 87, and how are they actuarially calculated?