The most common and most likely answer to this crossword clue is the 5 letter word BEANO
I've seen this crossword clue in Financial Times
B
E
A
N
O
More clues leading to the result BEANO
Buddy explains!

The straight part
We know that "a party" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a party = beano.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BEANO mean?
BEANO noun- A beanfeast; any noisy celebration, a party.
- Any home-made gas or indigestion remedy.