Daylight Amulet also called Daylight Ring is a piece of jewelry with a lapis lazuli gemstone enchanted by witches, to protect vampires from the sunlight thus, allowing them to walk freely in the day. Their werewolf counterparts are the Moonlight Amulets.
The witch who casts the enchantment can also temporarily or permanently undo the spell on the jewelry at their discretion.
Throughout the series, female vampires often wear bracelets, necklaces, or rings that possess a lapis lazuli gemstone, as opposed to male vampires, who usually just wear rings. The jewelry itself doesn't have to be worn as it was intended; as long as it the vampire is touching or holding it in some way, they are protected from sunlight.
The Mikaelson Family Rings are the first daylight rings in history, created by Esther, the mother of the family, and the Original Witch. Esther enchanted six golden rings with lapis-lazuli stones for the six members of the Original Family of vampires (also known as "The Originals"), they prevented one from burning in the sunlight.
Although the Originals cannot be destroyed by the sun, the sun will burn them before they heal. Without their rings in the public, they would expose themselves as vampires. Since they were the first of their kind, only the originals owned daylight rings, and for many decades, it kept up, until the spell to create the rings was slowly revealed, and more and more vampires started to wear Daylight Amulets. Either by form of rings, or other jewelry.