To me, glitch seems just a gaming-specific synonym for a software bug, especially one that:
- keeps the game running (this is probably the most important property);
- violates the intended game mechanics;
- results from a low-level problem such as overflow, race condition or memory corruption, as opposed to a logic error (e.g. sequence-breaking a puzzle);
- may require actions not usually performed in normal gameplay to be triggered;
- can be used to the player’s advantage.
Sometimes glitch is used in the meaning of ‘exploit’ instead, like in the expression perform the glitch.
Given that low-level bugs tend to happen more often in software written in low-level languages, and that includes most games considered ‘retro’, I figure there might be quite a lot of those that would fit within the scope of retrocomputing.
We don’t seem to have a tag for software bugs in general (not that there aren’t some questions for which one would fit, like the one about Y2K), but if one existed, perhaps glitches could be merged into it. But I can also see some value in keeping it separate.
Later: I have created bugs and applied it to a number of questions; in some, glitches would have clearly been inappropriate.