Originally "allegro" translated from Italian as meaning happy, cheerful, or joyful but it is more commonly used in music to indicate a fast tempo. I have no official scoop as to their oringinal intent but I would think that as an airline, they intended to imply "fast" or "quick".
Allegro is a Mexican charter airline that flies B-727's. They essentialy fly cabotage(sp?) here in the states. Most flights being between US and Mexico. They take away alot of business for american operators because they can charge very little. Very low mx costs and very low pilot pay allows them to out bid most US carriers. Mexico says they will allow US carriers to fly interMexico routes in exchange. Obviously there are no viable routes inside of Mexico.
They run charters (mostly for FunJet Vacations) to all the hot-spots in Mexico. There is a class-action law suit against them dealing with the cabotage issue mentioned earlier. Ya, like any of us want to fly point-to-point in Mexico. No thanks. We compete against them poorly as they run a dirt-cheap airline and offer dirt-cheap charter rates to the wholesalers. Poor passengers show up expecting ATA and get stuck on a butt-hole operator from Mexico, I think I'd take my family and leave!!!!!!!