A person who thrives on and enjoys activities which produce an adrenaline surge in that person. Such activities include cave diving, hang gliding, skydiving, skiing, snowboarding, wakeboarding, rock climbing with minimal equipment, stunt piloting of any vehicle, and other such things. AJ's are a sub-culture that is often viewed with dissaproval by mundanes, normals, and people who don't know how to have fun.