Which one is the message and which one the entity in HTTP terminology?

Question

I am trying to make better sense of HTTP internals, and often "entities" and "messages" are mentioned in the specification, strangely enough without proper explanation though, believe it or not. From what I gathered, one identifies the content itself, even when split across a request / response chain and/or transfer encoding fragmentation rules, while the other identifies content of a single HTTP request - i.e. what follows the headers and ends with a CRLF. My problem is I cannot figure out which one is which exactly.

Answer 1

A HTTP-message is either a request or a response:

  HTTP-message   = Request | Response     ; HTTP/1.1 messages

A HTTP-message has zero or more message-header⁠s and may have a message-body:

   generic-message = start-line
                     *(message-header CRLF)
                     CRLF
                     [ message-body ]

So not every HTTP-message has a message-body. But if it has a message-body, then that’s also the entity-body:

  message-body = entity-body
               | <entity-body encoded as per Transfer-Encoding>

So in short: A message is the whole HTTP request or response. And the entity is the message’s body (if there is any) and its corresponding entity header fields.