Small flap; computer key (3)
I believe the answer is:
tab
I believe this is a double definition.
'small flap' is the first definition.
(I've seen this in another clue)
'computer key' is the second definition.
(I know that tab is a computer key)
(Other definitions for tab that I've seen before include "Running bar bill" , "Bar tally; small flap" , "Ring pull" , "Small flap - bill" , "Flap; meal bill" .)