WordNet (r) 3.0 (2006):

webmaster
    n 1: a technician who designs or maintains a website

The Jargon File (version 4.4.7, 29 Dec 2003):

webmaster
 n.

    [WWW: from postmaster] The person at a site providing World Wide Web
    information who is responsible for maintaining the public pages and keeping
    the Web server running and properly configured.


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

webmaster
webmistress

    (Sometimes "webmistress") The alias or role
   of the person(s) responsible for the development and
   maintenance of one or more web servers and/or some or all of
   the web pages at a website.  The term does not imply any
   particular level of skill or mastery (see "webmonkey").

   The webmaster's e-mail address often appears on the home
   page of the site.  Failing that, you could try sending e-mail
   to postmaster (from which the term is probably derived) or
   root at that host, possibly after removing an initial
   "www.".

   (1999-04-01)