Some monsters are so huge and threatening that they are even more frightening than those described by the fear rules. These creatures cause terror. Troops confronted by monsters or situations that cause terror must test to see if they overcome their terror. Should they fail they will be completely overwhelmed with horror and reduced to gibbering wrecks. Troops only ever test for terror once in a battle. Once they have overcome their terror they are not affected again.
If a creature causes terror then it automatically causes fear as well, and all the rules described above apply. However, you never have to take a terror and a fear test from the same enemy or situation - just take a terror test: if you pass the terror test then you automatically pass the fear test too. As you only ever take one terror test in a battle. any subsequent encounters with terrifying monsters or situations will simply count as fear.
A unit must test to overcome its terror if charged by or wishing to charge an enemy that causes terror.
A unit must test for terror at the start of its turn if there is an enemy which causes terror within 8"
Remember that only a single test is ever made for terror by any unit during the whole game, whether it is made because of a charge or because the unit finds itself within 8" of a terror-causing monster.
A unit which fails its terror test will flee immediately, exactly as if it had failed its break test in hand-to-hand combat, or decided to flee from a charge.