Note: You are currently viewing documentation for Moodle 2.3. Up-to-date documentation for the latest stable version is available here: HTML.
HTML, along with PHP, CSS & SQL is one of the basic web technologies used to build Moodle. It can also be used to create Moodle content, though you do not need to know anything about HTML to use Moodle.
The HTML block allows you to add arbritrary HTML to a block at the sides of your Moodle screen.