ice age
noun
Definitions
A period of long-term reduction in the temperature of Earth's surface and atmosphere, resulting in the presence of major polar ice sheets that reach the ocean and calve icebergs.
Example: The earth is currently in the Late Cenozoic Ice Age, an ice age that began 33.9 million years ago with the Antarctic Ice Cap.
Any of several glacial periods (within a scientific ice age) marked by episodes of extensive glaciation alternating with episodes of relative warmth (interglacial).