Yildun is a dim star in the middle of the handle of the Little Dipper, or the tail of the Lesser Bear, depending on your preferred name for the constellation. Although the star is not very bright, it is easy to make out from a dark location because of its position. Yildun is placed right next to Polaris, the North Star, around which the whole night sky seems to revolve.
Yildun has many of the same attributes as the North Star. In fact, had Polaris suddenly vanished, its neighbour could have made a suitable substitute for navigating on those clear, starry nights. As second closest to the North Celestial Pole, 3.5 degrees away from it, Yildun is very near the sky's point of zero rotation. It is therefore circumpolar - in the northern hemisphere it is perpetually visible as far as 3 degrees north. This means that all through the night, the star will stay at approximately the same point in the north.
The name comes from the Turkish word for star, yildiz, which is remarkable. Firstly, it is the only star named in Turkish - most of the other names are of Arabic, Latin or Greek extraction. Secondly, it's rather an insignificant astral body to be given a name as if it's the only star in the sky. And finally, the Turks themselves gave the name Yilduz to its brighter neighbour Polaris. Nobody seems to know how our Yildun was named. My personal belief is that somebody simply shifted the Turkish name for Polaris one star to the left, and thus Yildun got its name.
Interestingly, the third named star in the Lesser Bear is called Kochab, which comes from the Hebrew word for star.
The star name has been distorted into variations like Vildiur and Gildun. It is also used as a starting point for the other faint stars in Ursa Minor that haven't been given names of their own - starting at "our" Yildun, which is called Delta, they are Yildun Epsilon, Yildun Zeta, and Yildun Eta. If you don't like using beautiful common names for stars, the scientific name for Yildun is Delta Ursae Minoris.
Some statistics may or may not be of interest. Yildun is an A-type star more than 180 light years away from the Sun. It is white, but may look greenish when seen with the naked eye. Its magnitude is about 4.4, which in case you didn't already figure, is quite low. The temperature aboard the star is 9000 Kelvin, and it is 47 times more luminous than the Sun. Its spin speed is really fast, at 174 km/s it is 87 times faster than the sun and makes a full rotation in 19 hours.
Yildun doesn't appear to have been named in any other culture - the Greeks referred to it as the First Dancer because it was the star that circled Polaris the closest, and the ancient Chinese gave it a role as Imperial Guard for the Emperor of the Sky - which is none other than our old friend, Polaris.