One of the many words that Australians have cut syllables off and replaced with "-o". This one represents the hours after 12pm, and is used by people, who can't be bothered saying "-fternoon".
Hey Davo, I'm goin' to the servo for arvo smoko.
Translation: David, I'm going to the service station to purchase some food for the afternoon break.
The following user(s) said Thank You: Heidijo, michaelp