几天 (jǐ tiān) literally combines 几 (jǐ), meaning 'how many' or 'a few', and 天 (tiān), meaning 'day(s)'. Together, it functions as a quantified time expression that can mean either 'how many days?' in questions or 'a few days' in statements—its meaning depends entirely on context and sentence structure. It is an indefinite quantifier for short durations, typically implying three to seven days, not a precise count.

This phrase commonly appears in casual spoken and written Chinese when discussing short-term plans, recent events, or brief periods of time. It often follows measure words like 这 (this), 那 (that), or 前 (before), as in 这几天 (these past few days) or 前几天 (a few days ago). Unlike exact numbers (e.g., 三天), 几天 carries vagueness and informality, making it unsuitable for formal reports or strict scheduling contexts.