It's a gift for people after a party (8)
I believe the answer is:
'it's a gift' is the definition.
(donation is a kind of gift)
'people after a party' is the wordplay.
'people' becomes 'nation'.
'after' says to put letters next to each other.
'a party' becomes 'do' (do is a kind of party).
'nation' after 'do' is 'DONATION'.
'for' acts as a link.
(Other definitions for donation that I've seen before include "Money given to charity" , "presentation" , "Do anoint by way of a gift" , "Gift of money as to charity" , "present" .)