夏季 means 'summer season' — the warmest of the four traditional Chinese seasons, typically spanning June, July, and August in the Gregorian calendar. The character 夏 (xià) specifically denotes 'summer', carrying historical and cultural weight as one of the earliest named seasons in Chinese texts; 季 (jì) means 'season' or 'quarter of a year', often used in compound nouns like 春季 (spring), 秋季 (autumn), and 冬季 (winter). Together, 夏季 is a formal, standard term for summer, commonly used in weather reports, academic contexts, official documents, and seasonal planning.

Unlike colloquial alternatives like 夏天 (xiàtiān), which feels more conversational and emphasizes daily experience ('summer days'), 夏季 stresses the seasonal period as a measurable, calendrical unit. It frequently appears in phrases such as 夏季旅游 (summer tourism), 夏季服装 (summer clothing), and 夏季作息 (summer work/school schedule). It’s neutral in register and appropriate in both written and spoken formal settings.