Face is the celebrity, musician, model or image that visually represents an RP character, place or group. Usually, a character will keep they same face although they may change aspects (such as eye color or hair color) of the face, Canon characters commonly use the actor who portrayed their character in a film or on TV. Original characters and characters from books or other media that have not yet been adapted to film often select the performer they would like to see cast as their character.
Avi, avatar and playby are other terms used interchangeably with Face. Which one you choose to use is personal preference and depends on what platform you are role playing on.