Regular seating area commonly not upholstered (8)
I believe the answer is:
standard
'regular' is the definition.
(similar in meaning)
'seating area commonly not upholstered' is the wordplay.
I cannot really see how this works, but
'seating' could be 'stand' (eg a stand in a football ground) and 'stand' is found in the answer.
'area' could be 'a' (maths abbreviation) and 'a' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for standard that I've seen before include "Established or accepted model" , "Grade" , "Conventional" , "Flying colours" , "Established model - flag" .)