胜诉 is a separable verb (离合词) meaning 'to win a lawsuit' — the object 诉 can split off from 胜 when aspect markers, measure words, or time expressions need to slot between the two syllables. You can say 胜了诉 ('won the lawsuit'), 胜过一次诉 ('won a case once'), but not 胜诉他 ('win him') — the subject who loses is introduced with 对 or 跟 (对/跟对方胜诉). The word is mostly used in legal or formal contexts.