It is actually a variety (breed or race) of the species Brassica oleracea, to which cabbage, kale, collards, broccoli, brussels sprouts, and cauliflower also belong.
It is known by many different names, like Navalkol, Ganth Gobi, and so on. But, it is most commonly known as Kohlrabi.
There are two main varieties of kholrabi, white and purple. However, internally, both the “white” (actually light green color) as well as the purple types have similar cream-yellow color edible flesh. Kohlrabi has a similar taste and texture as that of a broccoli stem or cabbage, but milder and sweeter.