We have worked to set up a categorization of images into several levels and types of nudity. This categorization has been built to be aligned with what our users expect, and to help you define custom moderation rules specific to your use-case.
Here are the high-level categories:
Sexual activity: this includes actual or simulated sexual activity with exposed nudity.
Sexual display: this includes explicit exposure of genitals.
Sextoy: this includes displays of sextoy that are not in active use.
Erotica: this includes displays of breasts, nude buttocks or the pubic region.
Suggestive: this includes situations that could be considered sexually suggestive but does not include full nudity or explicit sexual acts (person in underwear or swimwear, bare male chest, suggestive cleavage, etc.)
None: this includes cases where none of the above class is detected.