The 304 (Not Modified) status code indicates that a conditional GET or HEAD request has been received and would have resulted in a 200 (OK) response if it were not for the fact that the condition evaluated to false. In other words, there is no need for the server to transfer a representation of the target resource because the client already has a valid representation.

The server MUST NOT send a response body in a 304 response, and the client should use its cached copy. To update the cached copy, the server includes updated validators in the 304 response, which the client then uses for subsequent conditional requests.

This status is commonly used for efficient browser and CDN caching, reducing bandwidth and processing requirements for both the server and client.