Midsummer is the middle of summer: the weeks when, in a northern country, the days are longest and the weather is at its warmest. People also use it for a particular moment, the summer solstice, around 21 June in the north, when the sun is highest in the sky. Though actually the tidy calendar and the sky do not quite agree: in Britain, Midsummer's Day is 24 June, so 'the middle' is part season, part feast-day. In places such as Sweden, Midsummer is a big outdoor holiday; English speakers know that even if they do not keep the same feast. You will also hear it in titles — A Midsummer Night's Dream — where it feels magical, a night when strange things can happen. 'Midsummer madness' is a joking way to say people are acting silly in the heat. It is an ordinary word, a little literary in stories, perfectly at home in talk about weather and holidays.