Webmaster is a loose term that is used for someone who is responsible for a website. Although there are some qualifications with Webmaster in the title the term Webmaster on its own doesn’t denote any particular qualifications or competence.
It is best to think of the webmaster as the technical contact for a website. Whilst others may be responsible for the content of a website the webmaster is the person to turn to with any technical difficulties with the site. However, with many smaller websites they may well also be responsible for both content and the technical side of things.