This word applies to any system thats connecting to another system and attempts to encrypt the communications channel otherwise falling back to unencrypted communications. This process requires no previous configurations of the two systems, so the OE process should run just fine on both systems.

• http://en.wikipedia.org/wiki/Opportunistic_encryption

Virtual Private Network

A virtual private network extends a private network through a tunnel to other computers. It is highly secure and uses encryption to port network activity under a tunnel

http://en.wikipedia.org/wiki/Virtual_private_network