A shuriken is a hand-held weapon used primarily by martial artists, especially those who practice the more secretive forms, such as ninjitsu. The school of training with this weapon is called shuriken-jutsu, although any number of other martial arts offer some training with throwing weapons.
There are two different forms: bo shuriken and hira shuriken. Historically, bo shuriken were created by sharpening common metal objects such as coins, nails or hair pins. The form was most likely to be carried by a ninja looks like a sharpened railroad spike. A ninja or Samurai warrior would carry several around his waist as a secondary weapon.
The second form, the hira shuriken, is probably better known to Westerners as a "Ninja star" or "throwing star." They are forged from metal disks into elaborate stars with multiple points. Some are formed into sharp-edged "playing cards." Many feature a hole in the center, ostensibly for threading several together, but also to improve its aerodynamics. Although the points of throwing stars are sharpened, they are not considered deadly weapons.
A shuriken is considered to be a secret weapon, so its proper use is connected with stealth techniques. Throwing one at an opponent is meant to create confusion or a temporary nuisance, allowing the thrower to assume a more assertive position. In a sword fight, for example, a combatant may take several steps back from his opponent, reach inside a hidden compartment for a bo shuriken, then quickly throw the spike at his opponent's face, throat, hands or feet. While his opponent is temporarily distracted, the thrower can produce his sword and step in for a fatal strike.
Another use for this weapon is close contact fighting. The shuriken can be used as a dagger to injure the opponent or to stab him in an offensive move. Again, the success of this move depends on the element of surprise and quick access to the hidden weapon. Many of the martial arts forms taught in the school of shuriken-jutsu stress efficiency of movement and accuracy.
The use of hira shuriken or throwing stars is slightly different from bo shuriken techniques. The traditional Ninja star is often thrown much like a modern Frisbee, with a sharp snap of the wrist as it is released. This spinning action is intended to cause a slicing motion as the weapon hits its intended target. Sometimes, the throwing star is thrown much like a bo shuriken, with an overhead throwing style similar to a baseball pitch.