A Daylight Amulet 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 daylight.
The charm placed by witches over the gemstone is not dependent on the caster, since the lapis lazuli jewelry has been known to protect their vampire wearers long after the witch who spelled it have died. It was implied by both Stefan and Katherine that the enchanted jewelry only protects the vampire for whom the witch, who enchanted it, intended it to protect. Though vampires with daylight amulets are fairly common in the series, there are still many vampires who do not possess them, since most witches are not fondof vampires, and for that reason usually aren't willing to make them daylight amulets. Very few humans are aware of the existence of daylight amulets, either, which gives vampires the advantage of walking in the sun, avoiding suspicion from most humans who still believe vampires can only walk at night. When Stefan and Damon were interrogated about how they walk in the sunlight on separate occasions by Sheriff Forbes and Logan Fell, they both refused to tell their secret.
The spell to create a Daywalking amulet has been only seen once, when Bonnie made one to Caroline. The spell is without words, however the amulet need to be done with a Lapis Lazuli stone and be place in the sun light.
The written Spell was seen twice, when Klaus hided it at the Jardin Gris so Marcel could find it and another when Klaus give it to Davina so she could make one for Josh.
Bonnie explain that the witch who created the ring can also dispel it. However as it later shows, Travelers can undo the spell temporarily and Kai was able to destroy Elena's ring with using a melting spell.