For us, it is people who disappear without any notice or explanation. Be it from an RP or from the guild altogether. It doesn't take more than a couple of minutes to log on to say "Dropping out due to RL." or "RL issues. Be back in a month." or somesuch. People might not want to explain what their issue is (like what RL event caused them to have to drop, but that's their prerogative. For us at least, its perfectly fine if they just leave it at "RL."

Same goes when people drop out of an RP (but not off the guild). It doesn't take much time to throw in an OoC post stating that you're dropping. All GMs appreciate knowing whether someone's still in their RP.