Green’s Dictionary of Slang

(Aus., usu. teen) a party.

1960		A. Buzo Front Room Boys Scene i: Went to a turn at Collaroy. Some bird’s twenty-first.
1969		A. Buzo Rooted I i: bentley: How did you think the turn went? gary: It was a beauty. Best house-warming party I’ve been to.
2007		S. Maloney Sucked In 174: It was her wedding anniversary, one of the big ones. Her family was throwing a turn.