House edge
The cut a game is built to keep for the casino on average, shown as a percentage of what you bet.
The house edge is how much of each bet the casino expects to hold onto in the long run. Easy formula: 100% minus the RTP.
The price of playing
See it as the entry fee on every single bet. The more you bet in total, the more you should expect to lose, and that's why wagering requirements cost you money. On pure luck games, no system beats it. Provably fair doesn't shrink it either; it just proves nobody messed with your results.
Real-life example
A dice bet with a 50/50 shot pays 1.98x. A fair game would pay 2x. That gap is a 1% house edge: on average, you lose 1 $ every time you bet 100 $.
Usual numbers
Provably fair originals at crypto casinos tend to sit around 1%. Slots are all over the place, often 2% to 8%, depending on which RTP version the site picked. Table games depend on the rules and on how well you play.
Your expected loss
Total you bet x house edge. Say you deposit 50 $ but spin it around until you've bet 1 000 $ in total: it's the 1 000 $ that counts, not the 50 $.