What is glitch? is there an articel about glitch pokemon? I don't know yet..
Glitch is a kind of bug (may be causes by hacks, eg.). The glitch is, for example, BAD EGG (or isn't?). People who don't know shiny Pokémon may think that shiny Pokémon is a glitch. There are many glitches, but I really don't know even a few.
Ther are multiple glitches in the game. You can clone Pokemon, multiply your items through Missing No, and Bad Egg. In Ruby and Emerald, I have had the time stop.