Confidentiality

Confidentiality is the avoidance of the authorized disclosure of information.

It involves the protection of data, only providing access for people who are authorized.
The degree of confidentiality determines the secrecy of the information.

Encryption is the transfer of information using a secret encryption key, so the info can only be read using another key (the decryption key).

Authentication is the determination of the identity that someone has to decide whether access should be provided.

Ex: Google bot checker, verification codes, passwords, etc.

Physical security is the establishment of physical barriers to limit access to protected computational resources.

Ex: Windowless rooms, disallowing unknown signals to enter the enclosure (common measures of server rooms).