a "sex robot" is any artificial entity that is used for sexual purposes (i.e., for sexual stimulation and release) that meets the following three conditions:
Humanoid form, i.e., it is intended to represent (and is taken to represent) a human or human-like being in its appearance.
Human-like movement/behavior, i.e., it is intended to represent (and is taken to represent) a human or humanlike being in its behaviors and movements.
Some degree of artificial intelligence, i.e., it is capable of interpreting and responding to information in its environment. This may be minimal (e.g., simple preprogrammed behavioral responses) or more sophisticated (e.g., human-equivalent intelligence).
John Danaher, "Should We Be Thinking About Robot Sex?", in John Danaher & Neil McArthur, eds., Robot Sex: Social and Ethical Implications (Cambridge, MA: MIT Press, 2017), pp. 4-5
Danaher and other contributors to the book seem to use sex robot interchangeably with sexbot.