A webmaster is a person responsible for managing and maintaining a website. In the early days of the web, it referred to an individual who handled every aspect of running a website; in modern usage, it instead refers to a person responsible for overseeing its general operations.
The term "webmaster" comes from the role of "postmaster," referring to the individual in charge of running an email server. A webmaster maintains the web server with the website host to keep the website online. They are responsible for writing code that runs the website (both front-end languages like HTML and back-end languages like PHP or Perl) and adding content. A webmaster is also the primary point of contact for the users of a website, taking feedback from visitors and resolving the issues they bring up.
The term is no longer as common as it was in the early days of the Internet, where it was not only possible but routine for a single individual to handle all aspects of running a website. The technology required to run a modern website is more complex and requires a wide array of skills. It is now more common to delegate tasks amongst several team members with more specific roles and job titles.