There is a difference between a game glitch and a game hack though. A hack is when you look at a guidebook or game guide to find all of a missing item by location. Or it can be to find hidden items in a game that are placed there to be found for multiple reasons. A game cheat could also be a special code inserted into the game to give you items. An example of that is the famous code of "left, right, left, right, up, down, up, down, select and start."
A game hack is a mistake in the programming of the game. This is where the game itself was not really supposed to do that, but yet it does. An example of this would be an NHL Hockey game for the SNES system. There was a feature called "dump the puck hack" as one of the buttons. When you flew down the ice and hit the blue line after the red half line, and then hit the dump the puck button, the puck would fly in the air go over the goalies head and into the net for a goal.
These hacks can be quite fun as a single player to exploit and win a game. However they are not so fun in multiplayer games in which the glitch can only be accessed by one person or when it makes the game play no longer fun for everyone. However online gaming is a different playing field. If there is a glitch built into an online game, it can make life miserable for newer gamers. For those with experience though it can make the hack tool a blast. If the game has the programming to do something, then it is not cheating and should be used as much as possible.