Social gathering (3-8)
(Other definitions for get-together that I've seen before include "informal social gathering" , "Assemble" , "An informal party" , "Informal meeting" .)
'social gathering' is the definition.
(dinner party is a kind of social gathering)
This is the entire clue.
(Other definitions for dinner party that I've seen before include "Social gathering over a meal" , "social function" , "Sociable gathering for meal" .)