Information: a small amount brought back (4)
I believe the answer is:
data
'information' is the definition.
(data are bits of information)
'a small amount brought back' is the wordplay.
'a small amount' becomes 'atad' ('a tad' means a small amount of something).
'brought back' says the letters should be written backwards.
'atad' back-to-front is 'DATA'.
(Other definitions for data that I've seen before include "Known facts" , "Pieces of information" , "Contents of some banks?" , "Collection of bits of information" , "Collection of items of information" .)