Area of ground that’s holy, trimmed at the edges (4)
I believe the answer is:
acre
'area of ground' is the definition.
(acre is a measure of land area)
'holy trimmed at the edges' is the wordplay.
'holy' becomes 'sacred' (similar in meaning).
'trimmed at the edges' means to look at the middle letters (the edge letters are trimmed off).
The central letters of 'sacred' are 'ACRE'.
'that's' acts as a link.
(Other definitions for acre that I've seen before include "Measure of land area" , "4840 sq yds" , "region of ground" , "Care about the land measure" , "Crusaders battlefield, now in Israel" .)