'Brick' Refers to the MacBook Manufacturing Process
The MacBook manufacturing process up to this point has been outsourced to Chinese or Taiwanese manufacturers like Foxconn. Now Apple is in charge. The company has spent the last few years building an entirely new manufacturing process that uses lasers (w/o sharks) and jets of water to carve the MacBooks out of a brick of aluminum.9to5Mac speculates that this will give Apple strategic and technical advantages over other manufacturers, including improvements in complexity of case design, strength and quality. They also point out that Steve Jobs has been known to focus on the details of factory design with his NeXT startup in the 1980's.
The site also ties this back to recent comments by Peter Oppenheimer that Apple will continue to introduce state of the art products that their competitors are unable to match.
Finally, they expect that the MacBooks will indeed be released on October 14th.