Instructs clients no to cache the response in any way, and to forget it at soon as possible.
This directive was originally designed for sensitive data (today HTTPS should be used instead), but can be used to avoid polluting caches with responses that can't be reused.
It's appropriate only in specific cases where the response data is always different, e.g. an API endpoint that returns a large random number. Otherwise,
no-cache and revalidation can be used to have a behavior of "uncacheable" response, while still being able to save some bandwidth.