httpstatuses/contents/codes/404.md

set	code	title	references
4	404	Not Found	Rails HTTP Status Symbol :not_found

The 404 Not Found status code indicates that the origin server did not find a current representation for the target resource or is not willing to disclose that one exists.

A 404 status code does not indicate whether this lack of representation is temporary or permanent; the 410 (Gone) status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition is likely to be permanent.

A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of RFC7234).

Source: RFC7231 6.5.4