"Indian summer" is a period of unseasonably warm, dry weather that sometimes occurs in autumn in Northern America and other temperate regions of the world during late September to November.

In an article on the US National Weather Service's web site, weather historian William R. Deedler writes that Indian Summer can be defined as "any spell of warm, quiet, hazy weather that may occur in October or November."

The opposite of this is "Blackberry Winter". Blackberry winter is a colloquial expression used in south & midwest North America, referring to a cold snap that often occurs in late spring when blackberries are in bloom.