Outback hopper, informally (3)
I believe the answer is:
roo
'outback hopper informally' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for roo that I've seen before include "bounder" , "Jumping marsupial" , "Marsupial (dim.)" , "Diminutive inhabitant of Hundred Acre Wood" , "Aussie jumper!" .)