Web server
In computing, a server is a computer program or a device that provides functionality for other programs or devices, called "clients". Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers.
The computer that a server program runs in is also frequently referred to as a server (Server machine).
Web server
A web server is a computer system that processes requests via HTTP, the basic network protocol used to distribute information on the World Wide Web. https://en.wikipedia.org/wiki/Web_server
Apache
The Apache HTTP Server, colloquially called Apache, is the world's most used web server software.