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, myself included, who can't be bothered saying "-fternoon".
Arvo is a term used for a douchebag Russians who blame you for everything and try getting people killed. Arvos still gun people who sympathize and care for them and if caught, arvos cry for sister.