A mime is a performer who uses exaggerated facial expressions and body movements — instead of words — to communicate with his audience.
You may have seen a mime pretending she's trapped in an invisible box, using gestures to make it appear that she is pushing against walls and a ceiling. Many mimes also wear clown-like makeup, wear simple clothing, and refuse to speak. You can use the word mime as a verb as well, to describe what you do when you imitate your least favorite teacher for the amusement of your friends. The Greek root word is mimos, "imitator, actor, or buffoon."