A gift from Galadriel to Frodo at the departure from Lothlórien.

It was a small crystal phial: it glittered and rays of white light sprang from it. Inside of it was caught the light of Eärendil's star, set amid water. It shines brightest when night is about, and is a light to you in dark places, when all other lights go out.

When Frodo and Samwise traveled to Cirith Ungol and faced Shelob in her lair, this proved a most helpful gift, for it helped to defeat Shelob.
Encyclopedia entry originally written by KingdomWarrior