1. A hard confectionary treat of large sugar crystals formed around a stick or piece of string. My parents always get me a huge string of rock candy when we go to the county fair each summer.

2. slang Cocaine that is mixed with baking soda to form hard nuggets that can be smoked. There's some guy trying to peddle rock candy around the back of the high school. Hey man, got any rock candy on you? I'm jonesing hard.