Writing endless true rubbish in shabby atelier (10)
I believe the answer is:
literature
'writing' is the definition.
(I've seen this before)
'endless true rubbish in shabby atelier' is the wordplay.
'endless' means to remove the last letter.
'rubbish' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'shabby' indicates anagramming the letters.
'true' with its last letter taken away is 'tru'.
'tru' anagrammed gives 'tur'.
'atelier' is an anagram of 'literae'.
'tur' placed inside 'literae' is 'LITERATURE'.
(Other definitions for literature that I've seen before include "promotional material" , "Written works of artistic merit" , "writer's work" , "Printed matter" , "What author writes" .)