Broccoli Raab, what is it?

What is Broccoli Raab? Broccoli raab is a vegetable with many names.  In the U.S. is is most commonly known as broccoli raab or rabe.  In other countries, it may be referred to as Italian turnip, Italian broccoli, Chinese broccoli, turnip broccoli, rapine, and the list goes on and on....