Nazar Boncuk(nahZAR bohnJUK) is a Turkish good luck charm that protects one from the dangers of the Evil Eye. The closest translation to english would be "Evil Eye Charm/Bauble." The superstition of the Evil Eye is described that because of one's envy, they can cause harm. If a person looks on another person with envy, they might cause misfortune even if they don't mean to. From this superstition, the Turks made the Nazar Boncuk to protect against the Evil Eye by having another eye stare right back.
Generally, as an old custom, one gives a Nazar Boncuk to a baby so that they won't be harmed by the envies of those that come visit them. One also knows when a Nazar Boncuk has done all it can, by checking it for cracks. If it has a crack, then one is supposed to throw it out and get a new one.
The nazar boncuk is generally made of blue glass with a white circle within, representing the eyeball; then a yellow or blue circle, which represents the iris; and then a black circle, which represents the pupil. Small versions often leave out the colored area that represents the iris. So it generally looks something like this:
The Nazar Boncuk is so much part of Turkish fashion that you can find it on numerous pieces of art. You can find Nazar Boncuk necklaces, bracelets, hangings, keychains, etc. You can go to eBay, and search for Nazar Boncuk or go to http://www.business-with-turkey.com/tourist-guide/evil_eye_amulet_nazar_boncuk.htm to look at the different things that the Nazar Boncuk is used in. It has also become a popular tourist item to bring back.
I have two Nazar Boncuks hanging in my room, one above my computer and the other right across from the door. I also have quite a few keychains featuring the Nazar Boncuk in different styles. They're quite lovely, but absurd to carry around as keychains since they're made of glass. Like many people these days, I don't believe in the Evil Eye, but they're simply too great of a conversation piece and cultural piece to not have at least one.