先后 (xiān hòu) literally combines 先 (‘first’) and 后 (‘after’ or ‘later’) to mean ‘order’ or ‘sequence’—specifically the chronological or logical order in which things happen or are arranged. It functions as an abstract noun, often appearing after verbs like 分清 (to distinguish), 明确 (to clarify), or 决定 (to decide), emphasizing the importance of getting events or steps in the correct temporal or procedural sequence.

This word is commonly used in formal or instructional contexts—such as explaining procedures, analyzing historical events, or giving directions—where timing and priority matter. Unlike time words like 之前 or 之后, 先后 doesn’t refer to a specific point in time but rather to the relative positioning of two or more items within a series. It frequently appears in written Chinese and formal speech, and rarely in casual conversation unless discussing structure or logic.