Expression used in Greater Manchester (4)
I believe the answer is:
term
'expression' is the definition.
(I've seen this in other clues)
'in greater manchester' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TERM' is hidden within 'greater manchester'.
'used' is the link.
(Other definitions for term that I've seen before include "Expression, or period in which law court holds sessions" , "An expression or period in office" , "Word; trimester" , "Time spent at school" , "Part of the school year" .)