Arvo is a slang or colloquial term for afternoon, in Australia. It is moderately used in day-to-day life however it should be avoided in strictly formal situations.

Examples:

Appropriate uses:
"Yeah sure, I'll swing by this arvo to pick up Linux Mandrake 8.0".

"Got busted by the bofh this arvo for playing snes games in the CAD labs. What an asshole."

Inappropriate uses:
"We are all gathered here this arvo to see John Doe wed Jane Doe in holy matrimony."
Note that the first two examples happened to me today. Mandrake is sweet. End GTKYN .