The American Meteorological Society's Glossary of Weather and Climate defines Indian summer as: "A time interval, in mid- or late autumn, of unseasonably warm weather, generally with clear skies, sunny but hazy days, and cool nights. In New England, at least one killing frost and preferably a substantial period of normally cool weather must precede this warm spell in order for it to be considered a true "Indian summer." It does not occur very year; and in some years two or three Indian summers may occur."
Whatever you prefer to call it, yesterday was glorious. We were looking after our Granddog Sylvia and she walked our legs off at the park at the South end of our small city and form part of a trail that follows the shore of Lake Ontario.