Well, on a lot of sites, they'll label a boot "mountaineering boot." A mountaineering boot is made of hard plastic and ready to take any number of add-ons like crampons. Shoe and boot makers frequently label boots of leather and suede as such, but it's not what they are.... If you say to an old timer mountaineer "I'm getting mountaineering boots" you will confuse the heck out of him showing up with some of those heavy but not-mountaineering boots.

Labels shift around a lot. But to my way of thinking, you will never run in a mid height boot - so they may be the mid height version of the running shoe, but they aren't the same as trail runners. I had a pair of mid height Merrel Moab Ventilators that had a lighter sole than the Montrail trail runners, and am trying to get rid of them as they are too light to protect the bottoms of my feet. The trail runners have more aggressive traction as well. I was on a trail that crossed a stream 10 times within 8 miles - having the trail runners was a godsend, the water just poured out after each crossing, the wool ankle socks kept my feet warm even when wet, and no blisters whatsoever because the fit was right even tho there was damp in all day. Blisters happen with friction and dampness - no friction, no problem.

The goretex versions of trail runners are for walking in wet grass - after a few miles of that your socks are wet. Since I don't care and my feet sweat anyway, I prefer the more breathable non-gore.