折桂 is a literary set phrase meaning 'to win first place' or 'to come out on top'. It originates from the imperial examination system, where successful candidates were said to pluck a cassia branch (折桂). Today you can use it in formal or congratulatory contexts for any competition — academic contests, sports tournaments, or professional awards. It's a separable verb (离合词), so you can split it: 折了桂 ('won the championship').