Basic HTML documents
HTML documents are made up of text and images. HTML is used to mark up the text so that a web browser can render (or show) the text and images correctly.
HTML stands for HyperText Markup Language.
A markup language:
is invisible to final users (usually)
provides information about how, where and in what style a document will be displayed
can include other information (e.g. terms used by search engine
uses tags to mark up items
Simple HTML documents can be created using very few basic tags.
HTML was developed in the 1980s at CERN in Switzerland as a way of communicating ideas between scientists.
For more history see the History of HTML page.
For more information about HTML see the Wikipedia page on the subject.