Club in back of shed is firm (5)
I believe the answer is:
disco
'club' is the definition.
(I've seen this before)
'back of shed is firm' is the wordplay.
'back of' indicates one should take the final letters.
'firm' becomes 'co' (a firm is a company).
The last letter of 'shed' is 'd'.
'd'+'is'+'co'='DISCO'
'in' is the link.
(Other definitions for disco that I've seen before include "Modern dancehall of youth" , "Party with records" , "music supplier" , "Club or party with dancing" , "Style of pop music" .)