Private Pastes
Pastes on are public by default. This means that they are linked to in the "Recent Pastes" section, and from other pages on, and that they may be discovered by search engines.

If you mark a paste "private", it will not be publicly linked on, and will contain a noindex tag to advise search engines not to index it. This is a basic, minimally effective way of keeping pastes private: only users to whom you send the URL will be able to find your private pastes.