Operate on old boy outside - that's what has to be done (8)
I believe the answer is:
workload
'what has to be done' is the definition.
I can't tell whether this defines the answer.
'operate on old boy outside' is the wordplay.
'operate on' becomes 'work' (synonyms. I am not sure about the 'on' bit.).
'old' becomes 'o' (abbreviation).
'boy' becomes 'lad' (informal term for boy).
'outside' is an insertion indicator (some letters go outside others).
'o' placed within 'lad' is 'load'.
'work'+'load'='WORKLOAD'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for workload that I've seen before include "Task(s) for a specified time" , "What's on one's plate" , "Amount one has to do" .)