Orgy in the back bar (5)
I believe the answer is:
revel
'orgy' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for revel that I've seen before include "Lever (anag.)" , "Take part in lively and noisy festivities" , "Take great pleasure" , "Take great delight (in)" , "Celebrate noisily" .)