Winrate is the term that describes how much you beat the game. It is often mentioned in big blinds/100 hands or $/hour. This term comes from popular poker tracking software used by serious online players.
A 4 big blinds/100 winrate at NL25 simply means that you expect to win 4 big blinds per 100 hands you play at that limit on average. Your win rate is only meaningful over a large sample over the span of thousands of hands played.