Sunlight

The Sun is the star at the center of the Solar System. It is the brightest regularly visible celestial body in Earth's sky, the second being the Moon. Sunlight is one of the basic weaknesses of all vampires, including the Originals, having been a key ingredient in their creation.

Effects
Under normal circumstances, daylight can be harmful to Vampires. And depending on factors (i.e. the intensity of the light, length of exposure to it, along with how old and powerful the vampire in question).

The effects may range from merely causing the vampire to sizzle or steam, to incinerating them instantly on the spot. Vampires that are still in transition can resist the effects of direct exposure, albeit will be severely inconvenienced by it.

Unlike normal vampires, Originals are impervious to the sun. Although the sun can severely weaken an Original, they are unable to be killed by it.

History
Some vampires have spelled daylight jewelry with Lapis Lazuli; these rings must be forged by witches because the lapis itself is simply a stone. It protects them from the sunlight. So long as the vampire wears it in the sun, he or she can't die from exposure.