404.
Page not found.

SI-Q

What is the origin of the 404 error?

The same guy who made the modern Web page possible also invented the Page Not Found. The HTTP code 404 actually means two things: Client Error (the first 4) and Not Found (04). The 404 has become so common in modern culture that some young Londoners might label someone as “404,” meaning that person is clueless.

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