A local area network (LAN) server is a program (and by implication usually the computer it runs in) that "serves" the resources (files, storage, application programs, printers, and other devices) for a number of attached workstations.
In an enterprise, a LAN server has an administrator (or someone who fills that role) and typically LAN services and the setting up and administration of the local area network are managed on behalf of users but not directly by the users.
A LAN server can also be housed in a computer that has other servers such as a proxy server.
Novell makes the most widely-installed LAN server. However, Windows NT and other servers are also commonly installed.