E
ETag
An ETag (entity tag) is an HTTP header that serves as a unique identifier for a specific version of a resource. It is a crucial mechanism for efficient cache validation. When a browser needs to check if a cached file is still fresh, it can send the file's ETag to the server. If the version on the server is identical, the server can respond with a lightweight `304 Not Modified` status, telling the browser to use its cached copy without needing to re-download the entire file.
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