I need to know if "задница" is slang and/or offensive. Or is it appropriate in polite conversation.
It's not offensive (unless used as a designation for a person) and not slang but vulgar it is, not quite like
жопа оr worse, but enough to be avoided in a polite conversation.
Instead some literary/medical/anatomical terms are preferred or naming it with euphemisms.
It's not tagged as vulgar in the dictionary unlike
But none of the usage examples can be considered polite or decent
Some ways of moving from rudeness towards politeness in case referring to that body part can't be avoided:
- попа - a direct reference, often used in conversation with children or with a patient about an upcoming injection (informally; medically formal is "укол в ягодицу")
- мягкое место - used to describe comic situations, etc. - with some friendly irony
- (то, что) пониже спины (slightly informal, neutral reference)
As others mentioned,
задница is not an extremely rude word. You can hear it quite often in television (in a movie or TV series), but you should never use it in polite conversation, yes.
Some more examples about referring to that part of a body:
пятая точка - neutral word, one of the best ways to mention it in the polite conversation. Even teachers sometimes use this in schools jokingly.
попец - good word to use in friendly conversation.
Серёг, подвинься немного, ты своим попцом все печенья сейчас раздавишь.
The part of the body was considered a bit improper to mention. And the word was considered as the a decent way to speak about an indecent part of body. As all these decent euphemisms, it too, started to transgress into becoming rude, had already got a touch of being funny and a little bit rude in the first half of 20th century, but didn't become an indecent word. And, I think, never will, for the subject itself is no more considered indecent in the contemporary life and language, and even the most rude form becomes acceptable in and by the cultural speech, TV, literature and even poems for children,
Жопа есть, а слова - нет?!
So, now the word "задница" is not indecent or improper even a little bit.