Tab key function (6)
I believe the answer is:
indent
'tab key function' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for indent that I've seen before include "Official order" , "Make a requisition (for)" , "Requisition for stores" , "Deep recess; official requisition" , "Leave a space at the start of a paragraph" .)