Summer Bikini Beach Buttock

Connotations
The English word of Greek origin "callipygian" indicates someone who has beautiful buttocks. However, the qualities that make buttocks beautiful or well-formed are not fixed, as sexual aesthetics of the buttocks vary considerably from culture to culture, from one period of fashion to another and even from person to person.
In ancient astrology, various parts of the body were associated with signs of the zodiac - e.g. the buttocks to Libra (The Balance). Depending on the context, exposure of the buttocks in non-intimate situations often causes feelings of shame, embarrassment or humiliation in a non-exhibitionist subject, and embarrassment or amusement in a non-voyeurist audience (pantsing). Expressions such as being caught with one's pants/ trousers down or more explicitly in Dutch, "met de billen bloot" ("with bared buttocks"), use the image as a metaphor for non-physical embarrassment as well.
Willfully exposing one's own bare buttocks as a protest, a provocation, or just for fun is called mooning.