This seems to be the term du jour for MMA commentators to describe a certain set of hand skills.
My take on this is that to call it "dirty boxing" is simplistic and denegrating to the actual amount of skill it takes to be good at it.
If we were talking about a gloved professional boxing match, and a boxer was using illegal techniques, then you would call him a dirty boxer. This is obviously the source of the label.
But in the boxing ring, because of the nature of the game and the size of the gloves, there are only so many illegal techinques that are possible.
However, in the MMA arena those techiques are quite legal. With MMA gloves and open hands the possiblities of legal techniques is much larger.
To continue to call it "dirty" is simply inaccurate. Do we call submission/Catch wrestling, "dirty wrestling"? No.
I think that for the benefit of the sport the use of the word "dirty" should not continue. It makes it sound like someone is cheating. And for the competitor that has trained his ass off to have superior hand skills and is able pull of these skillful techniques under pressure, calling them "dirty" demeans the actual skillfulness.
In the days of Bare Knuckle Boxing, many of these "dirty" skills were completely legal. I think that there are enough monikers out there that there is no reason to call it "dirty boxing", when in fact it is boxing, fighting, fisticuffs, of the very highest level.