Princeton's WordNet

1. ice age, glacial period, glacial epoch(noun)

   any period of time during which glaciers covered a large part of the earth's surface

   "the most recent ice age was during the Pleistocene"

2. Pleistocene, Pleistocene epoch, Glacial epoch(noun)

   from two million to 11 thousand years ago; extensive glaciation of the northern hemisphere; the time of human evolution