A fancy name for a person that relays information between two or more parties and generally could care less about the interests or concerns of either side.
Chris (acting as liason): Dude, your ex is at the door and wants to talk to you. She says its "important".
John: Tell that bitch to go kick rocks.
Chris: Tell her yourself! (goes back to his own)
noun. Coordinating different parts to maintain a mutual cooperation.
I am a room liason for the event, making sure everything is going as planned.