Yes a chav is someone who is roughly the British equivalent of trailer trash. Chav / chavvy are terms you'd use to be rude about someone who is lower class. It's not nice, but I do sometimes use it, depending on who I'm talking about and to.
To add to Rox
Star's post, although
Courtney might have an upper-class vibe in the US, surnames as first names don't here, so
Courtney, which probably became popular after
Courtney Cox and
Courtney Love became famous could be seen as lower-class / chavvy here. I don't know any personally, but the kind of people I see on TV or know of who have named their kids that, do fall into that stereotype.