Role levels are how I would based a role's size by lines and camera time or by how much of the story they tell.

Level
1: Starring, a role that is featured in this case above the title
2: Co-Starring, a role with a good amount of lines bu that is not above the title
3: Large Role: less lines than Co-Starring but still a good sized role
4: Medium Role: a role with more than one scene but not a super large role
5: Small Role: a role with few lines and/or a single scene
6: Dancers and Singers: in this case there are no stunt roles. Credited people who sing and dance
7: Credited Extras: Single line or non-speaking parts that are credited
8: Extras: non-credited roles in the scene