之前 (zhī qián) is a noun meaning 'before' or 'ago', used to refer to a point in time prior to a specific event or reference point. It is more precise than 以前 (yǐ qián), which often means 'in the past' generally, and is less formal than 此前 (cǐ qián) 'prior to this'. Unlike 前 (qián), which can also mean 'front' (location), 之前 is purely temporal.