you hear chavs saying it all the time but i never know what it means, is it like "bruv" and such?

If you have to ask then its not worth explaining.

....

Blood or Blud means mate or bruv "Yo blud"

what i thought but i was never sure, cheers

It's short for blood brother:
http://en.wikipedia.org/wiki/Blood_brother

In modern times, a common blood brother ceremony includes having each person make a small cut, usually on a finger or the forearm, and then the two cuts are pressed together, the idea being that each person's blood now flows in the other participant's veins.

In addition to the danger of blood loss or infection, blood brotherhood-type ceremonies pose a high risk of hepatitis and HIV infection.

i donthave clue what you guys are saying

whats a blood when its anhome