"Right cross" originated from "right hand cross-counter". Simply it's a counter that crosses over your opponent's left hand lead. Recently some people have made the generalization that a right cross is the same as a right hook, that is not so. Say for instance, I slip inside of your jab and throw a right hook or a straight right to your body, in no shape or form can that be called a right cross, this is because my right hand is not crossing over your left arm. Knowing this both a straight right and right hook can be a right cross if it crosses over your opponent's left arm. The term is a little confusing because it used to refer to a counter to your opponent's jab/straight-left, nowadays it can be any right hand that crosses your opponent's left shoulder.