That is a really good question and one you might post in the new divers or basic scuba forum. But since you have posted it here, my definition, as it applies to Cozumel, would be one that has a pile of divers on board, most of whom have little diving experience, who pay little attention to their divers in the water, and who do little, if anything to extend their divers' time underwater. In fact they may do things to minimize that, like suggesting that everyone must ascent at a certain time or when one diver reaches a particular pressure regardless of what remaining divers have time/air left or taking them deep to run their NDL up. Or, as others have mentioned in this thread, vomiting large numbers of divers (usually unskilled) onto a reef where they flail. Or shoot to the surface because they can't clear their mask or whatever. Or the DMs aren't local, don't know the reefs and regularly turnover every few months. Take your pick! Others may chime in but those would be factors in my definition.