Plausible deniability is when you have a hidden datastream inside another encrypted one, as there's no way to prove it is or isn't there without the key. See: T

Plausible deniability is when you have a hidden datastream inside another encrypted one, as there's no way to prove it is or isn't there without the key. See: TrueCrypt. PFS means "If the server's private key is later compromised, it can't be used to decrypt past captured traffic".