Green’s Dictionary of Slang

1. a party, a celebration, usu. involving drinking.

1902		Bulletin (Sydney) 6 Dec. 36/2: Nipper got spliced yesterday, and last night he invited ‘the herd’ to have a ‘dance and general jollo.’ Towards 10 o’clock some of ’em mixed matters, and Nipper left ’em to it and came outside with a few of his cobbers.
1914		Sydney Sportsman (Surry Hills, NSW) 4 Nov. 2/4: All their houses turned to Jollos / Of a werry reckless kind.
1945		Baker Aus. Lang. 168: Australians have a fair selection of terms to describe drinking and drinking bouts, such as [...] jamberoo, jollo, perisher.
1955		N. Pulliam I Travelled a Lonely Land (1957) 63: As host for the approaching evening’s jollo, you figure out the amount of liquid your guests will require.

2. intense activity, not necessarily pleasurable.

1908

Bulletin (Sydney) 30 July 14/2: ‘’N’ ’re yeh goin’ t’ ’it Shinner w’en y’ sight ’im?’ ‘My oath, Mucker! If y’re down at th’ alley termorrer night y’ll see some jollo.’.