Covering a section inside environment (7)
I believe the answer is:
habitat
'environment' is the definition.
(I know that habitat is a type of environment)
'covering a section inside' is the wordplay.
'covering' becomes 'habit' (habit is a kind of covering).
'inside' says to take the centre.
The central letter of 'section' is 't'.
'habit'+'a'+'t'='HABITAT'
(Other definitions for habitat that I've seen before include "Environment in which an organism normally lives" , "Natural home of wildlife" , "Surrender" , "(Organism's) natural home" , "Home ground of an animal" .)