"Four-oh-four" is a well-known phrase in technology that refers to an error message that pops up on a webpage when it cannot be found. While this term is widespread, there are several synonyms that people may not know. Some common alternatives are "not found," "error 404," "page not available," "page not found," and "404 error." These synonyms are essential because they give website visitors an indication that something is amiss and assist technical support personnel in troubleshooting. Understanding the various phrases used to indicate that a webpage cannot be found is crucial to the success of any online business.