A brick (or pound) of extremely high quality heroin. Since it's practically a concentrate it is typically cut and mixed into lesser forms.

Brock may also be known as "whip," and "rock."
"Could that form of heroin be called 'Brick?'"

"No, it was a concentrated powder, its street handle is 'whip,''rock' or 'brock'."

"A brick of brock?"
by TheCroupierDeals December 29, 2006
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