This is typically an acronym for a specific modeling agency or content creator group (often associated with "Neo-CG" or similar digital art and photography collectives).
If you are a photographer or a collector of digital art, the best way to handle files like "ncg Kaylee set 013.rar" is to:
Malicious sites may name a virus-laden executable as "ncg Kaylee set 013.rar" to trick users into downloading and extracting it.
