WordNet (r) 3.0 (2006):

hypertext markup language
    n 1: a set of tags and rules (conforming to SGML) for using them
         in developing hypertext documents [syn: hypertext markup
         language, hypertext mark-up language, HTML]

The Free On-line Dictionary of Computing (30 December 2018):

Hypertext Markup Language
HTML

    (HTML) A hypertext
   document format used on the web.  HTML is built
   on top of SGML.  "Tags" are embedded in the text.  A tag
   consists of a "<", a "directive" (in lower case), zero or
   more parameters and a ">".  Matched pairs of directives, like
   "" are used to delimit text which is to
   appear in a special place or style.

   Links to other documents are in the form

    foo

   where "" and "" delimit an "anchor", "href" introduces
   a hypertext reference, which is most often a Uniform Resource
   Locator (URL) (the string in double quotes in the example
   above).  The link will be represented in the browser by the
   text "foo" (typically shown underlined and in a different
   colour).

   A certain place within an HTML document can be marked with a
   named anchor, e.g.:

    

   The "fragment identifier", "baz", can be used in an href by
   appending "#baz" to the document name.

   Other common tags include 
 for a new paragraph, ..
   for bold text, 
 for an unnumbered list, 
 for
   preformated text, 
, 
 .. 
 for headings.

   HTML supports some standard SGML national characters and
   other non-ASCII characters through special escape
   sequences, e.g. "é" for a lower case 'e' with an acute
   accent.  You can sometimes get away without the terminating
   semicolon but it's bad style.

   Most systems will ignore the case of tags and attributes but
   lower case should be used for compatibility with XHTML.

   The web Consortium (W3C) is the international
   standards body for HTML.

   (http://w3.org/MarkUp/).

   Character escape sequences
   (http://w3.org/hypertext/WWW/MarkUp/ISOlat1.html).

   See also weblint.

   (2006-01-19)