排字 is a separable verb (离合词) that literally means 'arrange characters.' It has two main uses: (1) in printing/publishing, it refers to typesetting or composing text; (2) in large-scale performances (e.g., stadium shows), it means forming characters or patterns with colored cards held by people in a formation. When separated, the verb 排 takes measure words or complements, and 字 follows: 排好了字 (finished typesetting), 排过一次字 (did the card-display once).