(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.".