Web Server
A web server is a program which serves web pages to users in response to their requests, which are forwarded by their computers' HTTP clients(Browsers).

All computers that host websites must have web server program.
Purpose of Web server
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A web server’s main purpose is to store web site files and broadcast them over the internet for you site visitors to see. In essence, a web server is simply a powerful computer that stores and transmits data via the internet.