An error message you get on the Web when the URL you type into your browser is considered an incorrect address. The way a browser finds Web pages is that it queries a Domain Name Server (DNS) and asks for the numerical IP address of the URL you typed. If it does not get a reply or if the two addresses do not match up, the DNS computer cannot take you to the Web site with that name. It happens when a person or a company moves their Web site to another server (propagation issues go into effect, which can take a few days), or when bills haven't been paid (for example, to the ISP who hosts the site, or to keep the domain name registered). It is an error reported on the server-side, meaning you (the user or client) did not make the error happen. However, there's always the chance you typed the domain name incorrectly.