Galley’s last place in cove, not part of the main action (6)
I believe the answer is:
byplay
'not part of the main action' is the definition.
I can't tell whether this definition defines the answer.
'galley's last place in cove' is the wordplay.
'last' says to take the final letters.
'place' becomes 'pl' (abbreviation used in postal addresses).
'in' is an insertion indicator.
'cove' becomes 'bay' (both can mean a coastal inlet).
The final letter of 'galley' is 'y'.
'y'+'pl'='ypl'
'ypl' put into 'bay' is 'BYPLAY'.
Can you help me to learn more?
(Other definitions for byplay that I've seen before include "Minor goings-on" , "Secondary action on stage" , "Stage business" .)