What does the cryptic crossword clue "Smaller group waggling bums outside royal party (10)" mean?

The wordplay uses an anagram. anagram of BUMS (synonym="BUMS") + KING (synonym="royal") + DO (synonym="party") = SUBKINGDOM The answer is SUBKINGDOM.

Smaller group waggling bums outside royal party (10)

Guardian Cryptic #29092 | 13 Down | 2023-06-09 flower