Not that I care about any of this stuff, but I thought I'd clarify this...
Actually, a glitch can also be something that happens in a game, which was not intended by the programmers. Actually, this type of glitch is a lot more common because we usually aren't aware/don't notice them.
The most common cases for glitch accusations in melee are the Wavedash.But most of the glitches and programming errors couldn't exist without specific programming.The JC grab for example; it reads the position of the knee bend animation to neutral,so when you grab before the animation is over,you are in a still able to grab while in a neutral position.
Basically,it goes like this in theory:
Jump=Neutral position(Grounded)
Exploit=Grab or U-smash
Jump=Neutral position(grounded)+Possible grab or U-smash=JC grab or U-smash.
Yeah,I know it sucks.-_-
Just take a look at pretty much any speed run of a video game; the player takes advantages of glitches galore, and the games don't crash. (In a Metroid Prime 100% completion run, he got the Space Boots in the first 30 seconds of landing on Tallon...I'm pretty sure the programmers didn't intend that.) A glitch can simply be a user taking advantage of the program doing something which the programmer did not intend.
Glitches seem to be more like unintentional malfunctions rather than an intentional exploit.But if it wasn't within the designers intention to exploit the program,then it would technically be a glitch.I don't really believe that most advanced techniques are glitches,but you could be on to something.
Maybe they did want us to exploit these things,considering that L-canceling was a glitch and was returned to Melee.Easter eggs maybe?
In the case of smash: Ice Climber glitch is a good example. And, IMO, I consider Ganondorf's ridiculous huge hitbox on his Thunderdrop to be a glitch, too.
The hitbox is THAT big? I may have to see the actual frames on the hitbox to study this.