Hypertext Markup Language is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets and scripting languages such as JavaScript.

Where to Learn ???

Here are some links so you can learn HTML free,

  1.  W3 School
  2.  MDN
  4.  Learn HTML
  5.  Tutorials Point
  6.  QuackIT

If you know other sites that are free, Fell free to add to the comment section.