Song: "What We Do" (2003)
Album: Philadelphia Freeway (Freeway Album)
First Meaning: If you know anything about drugs or the metric system, you know that a "key" is a kilogram of drugs. If you have ever listened to Jay-Z you know that he used to sell drugs.
Second Meaning: Jay-Z is a fan of your piano skills, Billy Joel. He just wants you to know that he can play, too.

Complex Says: 2042: A wizened Jay-Z embarks on a comeback tour, refusing to perform unless he provides his own piano lines. Reviews are mixed.

Is It A Double Entendre? English Professor Adam Bradley: [No Comment]