Identities
Identities, in the context of the Mac OS X Server Certificate Manager, are the combination of a signed certificate for both keys of a PKI key pair. The system keychain makes identities available to the various services that support SSL.
Self-signed certificates are certificates that are digitally signed by the private key of the key pair [...]

Setting a FileVault Master Keychain
You can set a FileVault master keychain to decrypt any account that uses FileVault to encrypt data. You should set a FileVault keychain to ensure that data is not lost in the event of a forgotten password. If you forget the FileVault account password, which is used to decrypt encrypted data, [...]