秋季 literally means 'autumn season' and is a formal, standard term for the third season of the year — autumn (or fall). It combines 秋 (qiū), meaning 'autumn', and 季 (jì), meaning 'season'. Unlike the more colloquial word 秋天 (qiūtiān), 秋季 is commonly used in official, academic, or calendar-based contexts — such as school terms (e.g., 秋季学期), weather reports, agricultural planning, or business cycles. It emphasizes the seasonal period as a defined, measurable unit rather than evoking imagery or feeling.

This term is neutral in register and widely understood across Mandarin-speaking regions. It appears frequently in written materials like textbooks, news articles, and administrative documents. While it can appear in speech, especially in formal or professional settings, everyday conversation tends to favor 秋天. The word always functions as a noun and does not take aspect markers or verb-like modifiers — it cannot be reduplicated or used predicatively without additional structure.