What is the origin of the idiom "Indian summer" and when to use it?

The idiom "Indian summer" has its origin in North America and refers to a period of unseasonably warm and dry weather that occurs in late autumn. The term "Indian" in this context does not refer to Native American culture but rather to the perception that these weather conditions were commonly experienced by Native Americans during their hunting season. This phrase has been used since the late 18th century to describe this specific weather phenomenon.