What Is A Feature?
‘A ‘feature’ is an actor who is identifiable on-screen, and booked to work directly with the director. And uses their skill to bring the character to life. This can be by interpretation of the script. Or as is often common in TV commercials, by delivering on-screen the emotions and reactions, in a meaningful and real life way.  A feature is shot in close up, and due to the importance of their role they can not be cut from the eventual project. IE: A Bond film without Bond.

What Is A Walk-On?
‘A ‘walk-on’ is an identifiable non-speaking artist (except that background speech or noise shall not be deemed to be speaking in this context) who shall be required to act individually in medium shot, or more closely, a special function peculiar only to the role, trade or calling that the character is supposed to portray and/or who, at the same time that his/her movements are recorded, is subject to individual direction and has a direct relationship with an actor (i.e. visual featured artist) who is performing his/her part as directed.’
 
What Is A Supporting Artiste?
Supporting artists provide background action. They may be directed by First or Second Assistant Directors, and are sometimes asked to deliver small amounts of non-crucial dialogue.