From Bulbapedia, the community-driven Pokémon encyclopedia.
Super Glitch is the nickname for a large amount of Glitch moves that exist in numerous hexadecimal slots in Pokémon Red and Blue. These moves generally have either no name, a number of glitchy symbols as a name, or the name of a Pokémon in one's party as its name. They can cause some rather strange effects, the most famous one of which being a chain of events including the music slowing down and stopping, the user's name changing to "(glitchy symbols) TM TRAINER DITTO," giving both Pokémon nearly infinite HP, and giving the opponent mutiple random status conditions. This sometimes causes the opponent to faint, and sometimes gives the opponent or the user random attacks that they didn't know before. It can also turn the opponent or the user into a different Pokémon. It is suspected that this happens because the attack scrambles some information in the game's RAM. After the battle in which Super Glitch was used, the game always freezes.  Almost anything done with this glitch move can and will result in the game freezing: viewing the user's second stat page, selecting it in battle, even replacing it with another move. Basically, anything that involves viewing the attack's name.
Many make the mistake the effects of attributing the side effects of Super Glitch to the user, the most common example of which being .4. Because .4 knows Super Glitch as a starting move, it is mistakenly believed to be extremely dangerous to one's game and save file, while in reality, .4 is no more dangerous than MissingNo. or 'M. In fact, a .4 acquired by trading a pPkMnp from Yellow Version will pose no threat whatsoever to the game.