Meaning "Ballsey", gutsy, bad-ass or fearless it is a reference to Major Motoko Kusanagi who is a character in the Ghost in the Shell anime and manga series who shares many of these traits. Generally used among surfers, trail bikers, skaters and other extreme sports enthusiasts.
"Whoa! Did you see him skate under that truck? That was Major Kusanagi!"
"Riding that wave was Maaaajor Kusanagi!"