Human or not they exist (6)
I believe the answer is:
beings
'human or not' is the definition.
I can't judge whether this definition defines the answer.
'they exist' is the wordplay.
I cannot quite understand how this works, but
'exist' could be 'be' (synonyms) and 'be' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for beings that I've seen before include "Living entities" , "Living things" , "Life forms" , "Sentient creatures" , "Living people" .)