1. Any of the geologic epochs characterized by an ice age. Thus, the Pleistocene epoch may be termed a “glacial epoch. ” 2. Generally, an interval of geologic time that was marked by a major equatorward advance of ice. This has been applied to an entire ice age or (rarely) to the individual glacial “stages” that make up an ice age. The term “epoch” here is not used in the most technical sense of a geologic epoch.