Horror marks give a very small chance of being assasinated by horrors, IIRC .1% per turn. Also in a battle where Horrors are present the horrors will try to attack any horror marked individuals first. If the spell astral corruption is active the chances of Horror assasinations increase.
Defense is, as somebody said, basically just a default order. If you ahve units in a province with a castle commanders with defend will remain in the castle when the province is attacked while patrollers will try to face the attackers.
Roger that on the Horror Mark, Johan, and thanks! Now, should I use the Ry’leh Star Children as Horror-Mark missiles, or should I try casting Astral Weapon on a poison sword? Hmm…
