Reading is totally about essence (4)
I believe the answer is:
gist
'essence' is the definition.
(I know that essence can be written as gist)
'reading is totally about' is the wordplay.
'about' says the answer is hidden in the clue (the clue goes around or about the answer).
'GIST' is hidden within 'reading is totally'.
(Other definitions for gist that I've seen before include "Substance or general idea" , "Substance of an argument" , "Essential idea" , "Key point" , "Main point of the matter" .)