the time of the year when the sun is hottest and the days are longest, between spring and autumn:
the long hot summer of 1976
The children play on the beach during the summer.
in (the) summer
Miriam likes to relax in her garden in summer.
We're going to Italy next summer.
a hot summer's day
a sunny summer afternoon
a three week summer vacation
The tourist season lasts through late summer.
Parts of Spain are extremely hot in high summer (=the hottest part of summer).
20, 50 etc years of age:
a child of eleven summers