Having cooked pork butts now for 25+- years, I knew a long time ago that the end of the butt opposite the bone is very special and has the most moist and tender meat imaginable. It was only 4+- years ago that I found out that it has a name, or is referred to as the "Money Muscle". I heard it from competitors and have since heard it talked about quite a lot among competitors. I'm not sure that Myron Mixon didnt make it a little famous by mentioning it on the first BBQ PitMasters show.
For competitions I'd always made certain that this piece received special attention, with just the right amounts of injection and rub, knowing that it was probably going to be on the very top of my pulled pork box (where I display the very best pieces). Since that time I've found out that some of this is regional. We'd almost never see sliced pork in this area, yet in other areas they'd consider it a sin not to slice the Money Muscle and display it all on its own. Either way, it's a wonderfully tender piece of meat if cooked correctly and can be the showcase of your pork cooking skills.
For identification purposes, it has a very distinct fat marbling characteristic. I could put words like stripes, etc. on it, but frankly a picture is worth a thousand words, so here are a few to help:
Then Todd (of Plowboy's) had supplied this picture a few years back of some butts in process:
I found a great article, although it's a little KCBS centric, on cooking butts for competitions and taking care of that wonderful Money Muscle:
I hope this helps.