What are Servers and Web servers?

A server is a computer program or device that provides services for other programs (known as Clients). The computer that a server program runs in is also frequently referred to as a server; that device may be a dedicated server or used for other purposes as well.

Servers can provide various functionalities, such as sharing data or resources among multiple clients, or performing computation for a client. A single server can serve multiple clients, and a single client can use multiple servers. In the client-server programming model, a server program awaits and fulfills requests from client programs, which may be running in the same or other computers; these servers are often categorized in terms of their purpose.

A Web Server, on the other hand, is a computer system that processes requests via HTTP, the basic network protocol used to distribute information on the World Wide Web. The primary function of a web server is to store, process and deliver web pages to clients.
The term can refer specifically to the software that accepts and supervises the HTTP requests, or simply to the entire system.