Definitions

Not an exact science - but this is how you might tell the difference between the three main categories. What is a Supporting Artiste, what is  a Walk On Artiste and what is a Featured Artiste

Background - Supporting Artiste:

A person in a crowd scene or in the background action.

Equity commercial definition:

Background artist is not required to give individual characterisation nor to speak any word or line of dialogue except that background speech or noise shall not be deemed to be dialogue in this context. A background artist is a person or member of a group contributing to the overall authenticity and atmosphere of a scene. The individual or individuals in the group may be dressed in clothing identifiable with the role, calling or trade selected for each by the producer or advertiser, and may be directed by the director to move and/or react as required on the set. Crowd noises can include community singing of well known songs where words do not have to be learned.

Walk On Artiste:

A step up from a supporting artiste, someone the viewer is more likely to identify as an individual, who may have a few words to say.

Equity commercial definition:

Walk-on artist 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 (ie visual Featured Artist) who is performing his/her part as directed.

Featured Artiste:

A step up from a Walk On, Another name for an actor. A cast part.

You might find it helpful to read through all these onset terms