What is HTML? Its definition

The HTML stands for HyperText Markup Language.

What is HyperText?

Hypertext is text which contains links to other texts. The term was coined by Ted Nelson around 1965 (see History ).

HyperMedia is a term used for hypertext which is not constrained to be text: it can include graphics, video and sound , for example. Apparently Ted Nelson was the first to use this term too.

Hypertext and HyperMedia are concepts, not products.

What is Markup?

Markup is detailed instructions, usually written on a manuscript to be typeset, concerning style of type and makeup of pages. 

So, HTML is concept of enhancing the visual appearance of the HyperText.