Filth, look, seen in most of plaza (7)
I believe the answer is:
squalor
'filth' is the definition.
(thesaurus)
'look seen in most of plaza' is the wordplay.
'look' becomes 'lo'.
'seen in' is an insertion indicator.
'most of' means to remove the last letter.
'plaza' becomes 'square' ('square' can be a synonym of 'plaza').
'square' with its last letter taken away is 'squar'.
'lo' going within 'squar' is 'SQUALOR'.
(Other definitions for squalor that I've seen before include "Dirt and untidiness" , "Dirty and unpleasant state (in which to live)" , "Sordid, neglected state" , "Unpleasant dirtiness" , "What could be filthy" .)