Hyper Text is the method by which you move around on the web — by clicking on special text called hyperlinks which bring you to the next page. The fact that it is hyper just means it is not linear — i.e. you can go to any place on the Internet whenever you want by clicking on links — there is no set order to do things in.
Markup is what HTML tags do to the text inside them.
HTML is a Language, as it has code-words and syntax like any other language.