Study post covering extremely useful discussion (12)
I believe the answer is:
consultation
'discussion' is the definition.
(consultation is a kind of discussion)
'study post covering extremely useful' is the wordplay.
'study' becomes 'con' (con can mean to study).
'post' becomes 'station' (a station is a post).
'covering' means one lot of letters goes inside another.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'useful' with its centre taken out is 'ul'.
'station' enclosing 'ul' is 'sultation'.
'con'+'sultation'='CONSULTATION'
(Other definitions for consultation that I've seen before include "discussions" , "Conference" .)