A web server is a computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol, over the World Wide Web. The term web server can also refer to the computer or virtual machine running the program.

In large commercial deployments, a server computer running a web server can be rack-mounted with other servers to operate a web farm.

The primary function of a web server is to deliver web pages to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and JavaScripts.

A client, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource, or an error message if unable to do so. The resource is typically a real file on the server's secondary memory, but this is not necessarily the case and depends on how the web server is implemented.

While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including file uploads.

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