a game genie/gameshark, yes, that is indeed cheating, because they activate functions that are not naturally in the games, and because they essentially altar the game's code itself as the game is loaded. You can seriously permanently screw up your games if you misuse them. i guess in that case its more of a moral issue, though i dont see a problem with it if its a single player game and you dont use it to screw over other people in multiplayer.
game that have built in cheat codes like a password screen, thats different, as that is a function that the devs WANT you to use.
game that have built in cheat codes like a password screen, thats different, as that is a function that the devs WANT you to use.