A crucifix is a cross with the figure of Jesus on it, usually shown dying, with arms out. If the cross is empty, we just call it a cross; once the body is there, it is a crucifix. Catholic churches, schools, and homes often hang one on the wall; many Protestant churches prefer a bare cross, as a sign that Jesus is risen and not still on the wood. The word is the ordinary name for that object, not a rare scholarly one. You would not use it for a plus sign, a Red Cross mark, or two roads that meet. Though actually, in casual talk some people say “cross” for both, which is why a careful speaker still keeps the two words apart.