A sysop is the person who runs a computer server. The term is used mainly in the world of bulletin board services (BBSs). In general, a sysop or system operator is one who runs the day-to-day operation of a server and the term suggests a person who is available when the system is.
A related term is administrator. In larger computer systems, the administrator manages security and user access while a system operator monitors and performs routine operations at the computer. In smaller systems, the administrator and sysop tend to be the same person.
Server
In the context of the Web, a server is a computer that's connected to the Internet. It "serves" Web pages to people who request them.
A server exists with relation to one or more clients. Typically on the Internet, a larger, more powerful computer (such as a mainframe computer) is a server, and a smaller computer (a workstation at an office, for example) is a client. However, the reverse can be true, depending on the service being rendered.
Michael Devitt