Kohlrabi is in the cabbage family, and though it looks like a root it actually grows above ground. It is probably the vegetable we get the most questions about, and is least likely to be recognized. "What is that thing that looks like a UFO/Alien in my CSA share?" most people ask.
The way WE eat it most often (there are many different possibilities, this is just one) is to chop off the leaves and peel the green skin off with a knife. Then we slice the white crisp inside into chip-like pieces and eat it raw. It makes a great chip with hommous or other dips. You can also chop it up and put it in a stir-fry, it gets a nice juicy crunchy texture like a water chestnut.