A webmaster is someone who creates and manages the content and organization of a website, manages the computer server and technical programming aspects of a website or does both.
Companies advertising for a webmaster vary in their use of the term. In a smaller company, a webmaster typically takes care of all the technology related to the website. In a larger company, a webmaster tends to be someone with knowledge and experience with HTML or a more technical person with some programming skills. The technical webmaster runs the server (for example, by managing the creation and authorization associated with file systems) and writes programs or Practical Extraction and Reporting Language scripts required by the website.
In a very large corporation, there may be a webmaster team of people at the top of the corporation who establish the overall corporate site design and policies, arrange the necessary technical resources (working with the people who provide the corporation its network infrastructure), and supervise the design of the corporation's website (which is often done by an outside firm). At division and product levels, there may be additional webmasters who organize and develop the site content and programming for their division or product. In addition, there is likely to be an interrelated effort to create a site design, organization, and content for the corporation's intranet.
At a small corporation, the webmaster may be in charge of creating the site and putting it on a separate company's server or setting up one within the company. The site design and creation may be done initially by an outside design firm that turns the finished site over to the company's in-house webmaster to maintain and perhaps add content within the established design.
And if you are a firm that specializes in creating Web sites, you may refer to the overall producer or art director as the webmaster for a site.