Indestructible is a permanent ability that makes it so the card cannot be destroyed by damage or destroy effects. If a card has Indestructible as an ability, and an opponent uses Terror on that card, the targeted card is not destroyed. Indestructible frees it from death by damage and "kill" effects. However, the card can still be destroyed by means of forcing a sacrifice or just sacrificing in general. If a Legendary Creature is out on the field, and it's Indestructible, and another is played, both cards are sacrificed.