Ask a cockney. :))))

It's rhyming slang. In London I heard people shouting this from time to time. One person would shout "Oi Oi", [ meaning Hey! Hey!]and then the other would shout back SAVELOY! [ meaning a sausage] It must be done in loud voices, as far as I can make out. The Australians are famous for chanting "Aussie, aussie, aussie! Oi! oi! oi!"at international sporting matches to barrack for the Australian sportsperson or team.

The phrase is used as "friendly greetings", usually a person seeks your attention when he/she says it. It is a very low-class expression though. :))) Hope, it helps!

Contrary to popular belief, 'saveloi' (as it was originally spelt) was a small dog with an elongated torso that was popular in the courts of late-Tudor England. It was considered over-familiar for visiting minor nobility greet the lord or monarch upon arrival at the castle, and so this dog would be greeted in their stead, using the phrase 'oi oi'. Commoners found the custom absurd, and so took to greeting each other by shouting ''oi oi saveloi", which was later change to "saveloy" in the late 19th century when fish and chip shops began to sell sausages that were named for their resemblance of those aforementioned dogs.

A savaloy is a type of sausage often served in fish and chip shops. I have no idea what the phrase means though.