Why is a 99 called a 99?

"99 Problems" is a single released by American rapper Jay-Z in 2003 from the The Black Album. It reached number thirty on the U.S Billboard Hot 100 singles chart. The track was produced by Rick Rubin, his first hip hop production in many years. Rubin provided Jay-Z with the type of stripped-down beat that was once his trademark. The song features a sample of "The Big Beat" by Billy Squier.