The arithmetic
What is a casino house edge?
The house edge is the percentage of every dollar staked that the casino keeps over the long run. Single-zero roulette is 2.70%, blackjack played correctly is about 0.5%, keno can be 25% or worse.
It applies to turnover, not to your deposit, which is why a hundred dollars can produce far more than a hundred dollars of edge before it is gone.
Where the number comes from
It is the gap between the true odds of an outcome and what the game pays for it. A single number on a thirty-seven pocket wheel is 36 to 1 against and pays 35 to 1. That missing unit, spread across thirty seven spins, is 2.70%.
Nothing about that gap is hidden or unfair. It is the price of the entertainment, printed in the rules of the game, and it is the same for everybody at the table.
Edge times turnover times pace
Edge alone tells you almost nothing. Multiply it by what you stake and by how fast the game goes and you get the real cost.
A 1% game at C$10 a hand, two hundred hands an hour, is C$20. A 4% game at C$0.50 a spin, six hundred spins an hour, is C$12. The cheaper-sounding game is the more expensive one because of the pace.
Where the edge changes
Blackjack: ruleset and your decisions. Roulette: which wheel. Video poker: paytable. Slots: which build the operator licensed.
Sports betting is the exception. There the margin is set by the book rather than by the rules, which is the only corner of gambling where shopping around genuinely moves the number.