HTML is an acronym for "hypertext markup language" -- the kind of encoding that makes textual display of this sort possible. It is the standard for the WWW. There is an always-available on-line primer of the codes and syntax you need to create such documents, which you will find very easy to follow. It is in some ways a subset, much simpler, of the more ambitious SGML ("standard generalized markup langauge") promoted by many serious students of e-texts (including the Text-Encoding Initiative group or TEI) as a way of presenting texts "marked up" to facilitate the most sophisticated kind of searching and retrieval -- the powerful search engine that asks the OED so many interesting questions depends on that text having been prepared in SGML. There are other formats that compete, notably those that depend not on analyzing the text but on describing the page on which it appears -- "postscript" and "Acrobat" (a registered trademark of Adobe Systems) are two of these systems.