Hypertext is text which is not restricted to being linear. It contains links to other texts and other media. It branches like Choose Your Own Adventure books but can have millions of choices.
The term was coined by Ted Nelson around 1965.
Hypertext also refers to a form of electronic writing, an information technology, and a mode of publication. "By hypertext," Nelson explains, "I mean non-sequential writing—text that branches and allows choices to the reader, best read at an interactive screen." (Italics mine.)
HTML, the Hypertext Markup Language, was conceived as a way to do this "non-sequential writing" Nelson described.
All of this sounds very dry and academic but it isn't. Hypertext is where the magic lies.
The simple act of clicking a link (or tapping a link on a tablet device) can do something as mundane as providing a definition for a word or as exciting as taking you to another part of the planet.
A hypertext anchor tag starts with: <a href=
add a destination URL: "http://traveloutbackaustralia.com">
and an onscreen representation for the link: Another Part of the Planet
Then close the anchor tag: </a>