means A long geological period when global temperatures dropped enough for massive ice sheets and glaciers to expand across large parts of the Earth's surface.

from A transparent compound of plain English words: "ice," from Old English īs (with cousins across the Germanic languages, like German Eis), and "age," which came through Old French from Latin aetas, meaning a span of life or time. The term entered scientific English in the 1800s as geologists began recognizing that glaciers had once reached far beyond their present limits — a translation of the German Eiszeit, coined by naturalists puzzling over boulders and scratched bedrock left stranded where no ice now sits.