A Bodyguard is a pro-town role in which the player protects another from a nightkill. However, unlike a doctor, a Bodyguard will be killed in the protected player's place. A bodyguard only protects the player against night kills - any other actions performed on them will typically still go through.
An Elite Bodyguard is a variation where the Bodyguard not only protects the target and dies, but also kills the attacker in the process.
Some moderators announce when a Bodyguard died protecting the target (and occasionally who that target was!), while others keep it secret or just announce the Bodyguard died without attributing the cause of death.