1. A comparatively short period of warmth during an overall period of glaciation.
2. A period when a warmer climate separated two periods of glaciation and displayed a characteristic sequence of changes in vegetation.

The term is used especially for several such periods that occurred during the Pleistocene epoch, lasting from 1.8 million to 10,000 years ago.

3. A period of warm climate during the Pleistocene (and earlier glacial epochs) during which continental glaciers retreated to a minimum extent.

Interglacials have been of approximately 10,000 years duration, spaced at approximately 100,000-year intervals over the last 1,000,000 years. The last 10,000 years, or postglacial period, is generally considered to be interglacial.