The most common and most likely answer to this crossword clue is the 5 letter word SECTS
S
E
C
T
S
Buddy explains!

The straight part
We know that "parties" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case parties = sects.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 SECTS mean?
SECTS noun- An offshoot of a larger religion; a group sharing particular (often unorthodox) political and/or religious beliefs.
- A group following a specific ideal or a leader.
- A cutting; a scion.