A web server is a program that accepts HTTP requests from HTTP clients. When it receives a request, the web server examines the URI part of the request and responds accordingly. A URI can specify an action to perform, a file to be returned, or a script or program that the web server should run to generate the response. After finding the file, running the program, or performing some other action, the web server generates an HTTP response and returns it to the client.

A web server is not limited to processing requests one at a time. A web server is capable of processing a large number of requests simultaneously.