Entry made by Walter shortly appearing in a social gathering (10)
I believe the answer is:
admittance
'entry' is the definition.
(admittance is a kind of entry)
'walter shortly appearing in a social gathering' is the wordplay.
'walter shortly' becomes 'mitt' (I can't justify this - if you can you should give a lot more credence to this answer).
'appearing in' means one lot of letters goes inside another.
'social gathering' becomes 'dance' (dance is a kind of social gathering).
'a'+'dance'='adance'
'mitt' inserted inside 'adance' is 'ADMITTANCE'.
'made by' acts as a link.
Can you help me to learn more?
(Other definitions for admittance that I've seen before include "What bouncer controls" , "Letting in" , "Right to enter" , "Entry" , "gives one the right to be there" .)