Chris Rock is a very high-grade form of crack cocaine. While crack is generally considered a "ghetto drug", Chris Rock is thought of as a sort of gourmet crack that is favored by television stars and other celebrities.
The name refers to an infamous crack den once owned by Newsradio and King of the Hill star Stephen Root. Root's Chris Rock House, as the den was known, was instrumental in popularizing the drug in the late '90s. It quickly gained a reputation as a stylish hangout for the young and beautiful, and was for a time considered the place to be seen smoking crack.
Once asked where the "Chris" in the name came from, Root replied, "No clue. The name came with the place, so I kept it."