An erotic actor or erotic actress or a porn star is somebody who appears in pornographic movies. Many actors/actresses may appear nude in films (usually rather briefly) or on stage but even if they depict sexual behavior they are not considered erotic actors. Most erotic actors use stage names.
... complete the square[?]. To "complete the square" is to add a constant (i.e., in this case, a quantity that does not depend on x) to the expression to the left of ...