According to Urban Dictionary, "speed" is a slang term for amphetamine, a stimulating drug that triggers the brains reward system giving the user feelings of pleasure. It is also used as a generic slang term for a wide variety of stimulant drugs, mostly methamphetamine. "Street speed" is a more potent, cheaper, and possibly addictive form of amphetamine that is more common in Europe than in North America. Amphetamine is a drug that is used to treat ADD in hyperactive children, but it is also used by adults as a stimulant and is often abused. It can be taken in pill form once a day, like a vitamin, but one that makes you think, move, and talk faster.