Summer与spring，autumn， winter为表示季节的词，可作不可数名词，也可用作可数名词。

Many people prefer going bathing in the river in summer.（泛指夏天，用作不可数名词）The year 2022 saw a very hot summer. Summer也可以指全盛时期。eg.The tang dynasty is think of as the high summer of chinese poetry.