The Collaborative International Dictionary of English v.0.48:

Postglacial \Post*gla"cial\, a. (Geol.)
   (a) Formed or occurring after the last glacial epoch of the
       Pleistocene period, or at a locality within the area of
       Pleistocene glaciation after the final disappearance of
       the glacier from the locality.
   (b) Of, pertaining to, or designating, an epoch after the
       last Glacial and before the Terrace epoch. [R.]
       [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

postglacial
    adj 1: relating to or occurring during the time following a
           glacial period