Cacheable

A cacheable response is an HTTP response that can be cached, that is stored to be retrieved and used later, saving a new request to the server. Not all HTTP responses can be cached; these are the constraints for an HTTP response to be cacheable:

The method used in the request is cacheable, that is either a GET or a HEAD method. A response to a POST or PATCH request can also be cached if freshness is indicated and the Content-Location header is set, but this is rarely implemented. For example, Firefox does not support it (Firefox bug 109553). Other methods, like PUT or DELETE are not cacheable and their result cannot be cached.
The status code of the response is known by the application caching, and is cacheable. The following status codes are cacheable: 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501.
There are no specific headers in the response, like Cache-Control, with values that would prohibit caching.

Note that some requests with non-cacheable responses to a specific URI may invalidate previously cached responses from the same URI. For example, a PUT to /pageX.html will invalidate all cached responses to GET or HEAD requests to /pageX.html.

When both the method of the request and the status of the response are cacheable, the response to the request can be cached:

http

GET /pageX.html HTTP/1.1
(…)

200 OK
(…)

The response to a PUT request cannot be cached. Moreover, it invalidates cached data for requests to the same URI using HEAD or GET methods:

http

PUT /pageX.html HTTP/1.1
(…)

200 OK
(…)

The presence of the Cache-Control header with a particular value in the response can prevent caching:

http

GET /pageX.html HTTP/1.1
(…)

200 OK
Cache-Control: no-cache
(…)