Joke about extremely unethical prison camp (5)
I believe the answer is:
gulag
'prison camp' is the definition.
(gulag is a kind of prison camp)
'joke about extremely unethical' is the wordplay.
'joke' becomes 'gag' (a gag is a joke or witticism).
'about' is an insertion indicator.
'extremely' suggests removing the centre (only the extremes of the word are used).
'unethical' with its middle removed is 'ul'.
'gag' enclosing 'ul' is 'GULAG'.
(Other definitions for gulag that I've seen before include "Soviet camp system" , "Soviet prison camps" , "Soviet forced labour camp(s)" , "Soviet political prison system" , "Former prison camp in the USSR" .)