Simple definition
The HTTP Content-Encoding header identifies compression or other content transformations applied to a response body.
Purpose and use
Content-Encoding identifies coding applied to an HTTP representation, such as gzip or Brotli compression.
How does it work?
A client generally advertises accepted codings through Accept-Encoding, then decodes content according to the received response.
Example and verification
Unreadable pages or corrupted downloads can result from compressed content with a missing, incorrect or intermediary-modified header.
Points to watch
Coding does not replace Content-Type, which describes the content's nature. Compression is not encryption and provides no confidentiality.
In short
Transferred content, coding headers and cache-variant handling must remain consistent.