This is the 2118th most frequent Chinese word.
夏季
Summer.
夏季 here refers to the summer season and is used as the subject of the sentence to describe its characteristics as a period suitable for vacations.
夏季是适合去海边度假的季节。
Summer is the season suitable for vacationing by the sea.
夏季 here is used to specify the time period during which the stated action or preference, eating ice cream, occurs.
在夏季，许多人喜欢吃冰淇淋。
During summer, many people like to eat ice cream.
夏季 functions as a possessive noun in this sentence, describing the typical temperature of the summer period.