Moratorium is a Legendary Gem in Diablo III. It can only be socketed into Amulets and Rings, and drops from Greater Rift Guardians.
Stats

Moratorium
Legendary Gem
Properties:
- 35% of all damage taken is instead staggered and dealt to the character over 3 seconds.
- Upgrade: +0.1 seconds stagger duration per Rank.
- Max: 18 seconds at Rank 150.
- 20% chance on kill to clear all staggered damage (Requires Rank 25)
Precious stones can sometimes be found among the peaks of Ivgorod. The harmonics of these gems, while in combat, are said to forestall death itself.
Notes
- Shields can absorb the damage-over-time effect.
- This includes periodic damage, making it apply more slowly.
Trivia
- Moratorium is a real-world term for stopping something that was previously ongoing; in fiction, this usually relates to death sentences.
- This is one of the five gems (the others being Mutilation Guard, Molten Wildebeest's Gizzard, Invigorating Gemstone and Esoteric Alteration) that offer defensive, rather than offensive, bonuses.
- The "stagger damage" effect likely comes from World of Warcraft, where it is a class feature of Tank-specialized Monks. The description adds to this.