For tagging purposes, headphones with a structure resembling Akiyama Mio's AKG K701.
Most of them happen to be AKG K-something, but some others (Q701 for example) have a similar look and structure and still count. Likewise, headphones technically in the K-series that don't share this look (such as K553 with a different headband) don't count. If you can think of a better name for the tag, bring it up in the forum.
Notable visual traits:
Large circular cups with a smaller circular section sticking out in the middle
Headband with a pair of almost-parallel sticks separate from the pad that rests on the head, usually with visible circular attachment points
