Junk guides picked up (4)
I believe the answer is:
spam
'junk' is the definition.
(I've seen this before)
'guides picked up' is the wordplay.
'guides' becomes 'maps' (a map is a guide to a place).
'picked up' says the letters should be written backwards.
'maps' backwards is 'SPAM'.
(Other definitions for spam that I've seen before include "Send unsolicited mail" , "Spiced ham" , "Uninvited email" , "unsolicited communication" , "Thoughtlessly send" .)