A reference sheet for non-lead, background characters — distinct from the Three-Panel Character Sheet used for principal actors. Rather than locking one individual's exact likeness across poses, an NPC sheet defines a recurring role or type so background characters stay consistent across appearances without needing to be the same modeled person each time: age range, general appearance, uniform, and lighting directives.
Example from the source: a toll-booth controller NPC sheet specified the age range, look, uniform, and lighting for that recurring background role before generating any scenes that needed one.