summer
Summer is the season between spring and autumn.
If you want to say that something happens every year during this season, you say that it happens in summer or in the summer.
The room is stifling hot in summer and freezing in winter.
The town is full of tourists in the summer.
Be careful
Don't say that something happens ‘in the summers’ or ‘in summers’.
Don't say that something happens ‘in the summers’ or ‘in summers’.