I think some people see this as a contentious question Detta, but I will do my best to enlighten you although I asked the same question myself not long ago and there was a huge row going on about it and I think people thought I was stirring it up.
I think a chav is a bit like Essex girl or Essex man (oh boy I can see trouble brewing now) someone who wears showy clothes and jewellery but has no taste at all.
it's been around in Newcastle for years. Generally used to describe thieving low-life who live in Fenham, Byker, Blyth etc etc. Before you Geordies start having a go at me, that's how a local described chav to me!
Chavs love to dress in the Burberry check, known in Newcastle as Chavva Tartan