Junk plans rejected (4)
I believe the answer is:
spam
'junk' is the definition.
(I've seen this before)
'plans rejected' is the wordplay.
'plans' becomes 'maps' (I've seen this in another clue).
'rejected' is a reversal indicator.
'maps' backwards is 'SPAM'.
(Other definitions for spam that I've seen before include "Electronic junk mail" , "Tinned meat - unwanted email" , "(Send) junk mail" , "Computer junk mail" , "Tinned meat made largely from pork" .)