Summer is the warmest season of the year, between spring and autumn. In the Northern Hemisphere, it is usually defined as the period between the summer solstice (year’s longest day), June 21 or 22, and the autumnal equinox (day and night equal in length), September 22 or 23. A period of exceptionally hot weather, often with high humidity, during the summer is called a heat wave. Such an occurrence in the temperate regions of the Northern Hemisphere in the latter part of summer is sometimes called the dog days.

Source: Britannica