What a drover drives (4)
I believe the answer is:
herd
'what a drover drives' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for herd that I've seen before include "Collection of swine" , "Group of people behaving like sheep?" , "Group of cows, elephants etc" , "pack" , "Drove" .)