What exactly is cocoa butter?

So last summer i spent a lot of time with my cousins, and my cousin had this block of white oily stuff and she told me it was "coconut butter", she said it was for your skin. I tried it almost everyday and my skin was super soft, shiny and beautiful. The thing is I think she mixed up "coconut butter" with "cocoa butter", but I'm not sure since it smelled like coconuts. I'd like to use the same thing for this summer but I'm a little confused… thanks for any advice or tips 🙂