Used on the East Coast of the U.S. to mean 100% Pure uncut caffeine powder. Commonly snorted, but can also be taken orally. Users should not take more than 1g/35 lbs of body mass.
When one partakes in the act of inhaling cocaine through the nostril. The "hoover" section of the saying comes from the vacuum brand, while schneef is a variation on the word sniff or to sniff. "Schneef" is slang for cocaine.