Aye, you got it one fella!
Tripod = 3 legs - tri = three
Monopod = 1 leg - mono = single
Monopods are more portable and better for when you have less space and a less stable ground. They also take less time to setup and look less gimpy lol.
However, they are not as stable as tripods for obvious reasons, you usually lean them against something, but even without doing this they can make the world of difference, especially at the telephoto end. A lot of pro's have converted to them nowadays.
Tis a good and well built piece of kit - I just have no use for it anymore. And its taking up space in my boot.