While there are certain genuine sorts who talk the talk AND walk the walk (usually raised in actual rough neighborhoods), the American "chav" is almostalways from an affluent suburb and descends from lilly-white, non-divorced, WASP parentage. The former is instantlyrecognizable by the "thousand mile stare" or "serial killer shark eyes" that they have. The latter is always recognizable by the "Chip n' Dales" male stripper air freshener that is hanging in their Mom's BMW (which they are trying to pretend is their own, and always refer to as "the Beamer").
A pound of marijuana (or kilo of cocaine or heroin) that is compacted into a cube, thus resembling a brick. This is a process that is usually done for the purpose of shipping and/or smuggling the substance.
see: Numerous Hip-Hop lyrics pertaining to "bricks" e.g. "Bricks on consignment", "I move mad bricks in the hood/on the block", "Chopping up bricks", "Cooking bricks".