RTP is the return to player percentage. Roughly speaking, if the RTP of a slot is 95%, then for every 100 rubles you roll in, in theory you should get back 95. But! This is in theory and in the long term. But in the short term, it all depends on your luck.
True, theoretically. But don’t forget about volatility – it also plays a big role. A high RTP with low volatility will give you frequent but small wins. And high volatility is rare, but large.