Clue: Welcome to the Northern Territory (4)
I believe the answer is:
hint
'clue' is the definition.
(I know that clue can be written as hint)
'welcome to the northern territory' is the wordplay.
'welcome' becomes 'hi' (both are greetings).
'to the northern territory' becomes 'nt'.
'hi'+'nt'='HINT'
(Other definitions for hint that I've seen before include "Piece of advice" , "Intimate" , "Tip, clue" , "Indirect clue" , "Taste" .)