Easy one! An actor is the person you see playing the character. He or she is on your screen, unlike producers/directors/writers who work Behind the Scenes. One example is McMahon High's own, Mitch Longley. He played Mitch "Sassy" Sassen on Las Vegas!
extra
yes
scene a structure in which an actor could change masks or costumes SK(APeX)
The costume an actor is wearing
Supernumerary
The 'lead' investigating officer/detective is in charge regardless of who is "working" the scene.
David Ramsey
Such an actor is called an "extra." They are used in crowd scenes or where numbers of anonymous people are otherwise needed in a scene.
Orson Welles
Are you talking about the girl from My Music? I love that show! The actress is Lainey Lipson.
It is Selena, Just with a hair cap and wig.
Steve Buscemi