Blue and RyanL are correct so now you know what it is. So let me tell you a bit about the positives and negatives about it.
The positives were mentioned by Blue, it is cheaper than a dedicated server, and it is easier to learn on that a dedicated server. You can also have root access to the server, so it is better than a shared server, and there probably aren't as many accounts on a VPS machine as there are on a shared machine.
The negatives are, you share your resources, suach as CPU, RAM, B/W. This can cause bottlenecking. If you are planning on hosting something which requires high bandwidth usage, like video streaming, then VPS might not be the route you want to take. Also, with all of the users rooting in, and sharing your resources, your sites may be sluggish at times, and it may also go down because of someones else mistakes. Another thing is, because it is manage, you are not as free to do what you want as far as updates on software and other things, as you would be with an unmanaged dedicated server.
