The Collaborative International Dictionary of English v.0.48:

Pousse-caf'e \Pousse"-ca`f['e]"\, n. [F., fr. pousser to push +
   caf['e] coffee.]
   A drink served after coffee at dinner, usually one of several
   liqueurs, or cordials, of different specific gravities poured
   so as to remain separate in layers; hence, such a drink of
   cordials served at any time.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

pousse-cafe
    n 1: small drink served after dinner (especially several
         liqueurs poured carefully so as to remain in separate
         layers)