HTML
The code for creating webpagges, using tags and other commands that a browser reads and converts into the normal webpages that people see.
or <h1> to create websites. It might as well be the skeletal structure of the internet's completely hypothetical body. Since writing with just HTML doesn't make for very good websites, it works with another programming language called CSS to design things like fonts, colors, and other things that just bare HTML can't do.
HTML is on it's fifth edition, and is still being worked on.
It can't be used for making things like applications or video games. For those, programmers would use C++, C, Python, Ruby, Java, BASIC, or other things that you might be able to think of.
It also can't be used to make any interactive things except for hyperlinks. You'll need something like JavaScript for that.