收尾 is a separable verb (离合词) meaning 'to wind up, to finish' or 'the ending part (of a project, article, event, etc.)'. The verb 收 ('collect, close') and the noun 尾 ('tail') can separate when adding a complement, measure word, or modifier between them — for example, 收了一个漂亮的尾 ('had a beautifully wrapped-up ending') or 收不了尾 ('can't manage to wrap up'). It commonly refers to the final phase of construction work, the concluding section of a piece of writing, or the closing moments of an event.