Office work - binding, including third of reports (6)
I believe the answer is:
typing
'office work' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'binding including third of reports' is the wordplay.
'binding' becomes 'tying' ('tie' can be a synonym of 'bind').
'including' is an insertion indicator.
'third of reports' becomes 'p' (3rd letter of 'reports').
'tying' placed around 'p' is 'TYPING'.
Can you help me to learn more?
(Other definitions for typing that I've seen before include "Using one form of keyboard" , "Keyboarding" .)