House edge is a term that refers to the profit that a casino will earn from player action. Each slots game has a payout percentage. Most online slots games have a payout percentage of 90% or more. That means that 90% of the money put into a game will be paid back out in winnings to random players. The remaining 10% is the profit, or house edge. Every game in any casino holds a house edge, some games more than others.
These percentages are averages over a large number of spins, and it�s unlikely that a single player would experience getting back 90% of what they put into a game during a single session. If they played long enough the number would get closer to 90%, but in one session a player can experience just about any percentage of loss or windfall. It all depends on being the lucky one in the game when it pays out.