Seppuku is a Japanese ritual suicide, and was a common practice among samurai.
Seppuku is a part of the Bushido, the samurai code of rules. It is a voluntary act warriors used to avoid falling in enemies' hands or to atone for breaking the rules or making something dishonorable, thus dying in a respectable manner.
Before seppuku, the person drank sake and wrote a farewell poem called yuigon on their tessen (fan used in battlefield).
In the ritual, the person committing seppuku, dressed in white (color of mourning in Japan), opened his kimono, wrapped the blade of his tantô or wakizashi in rice paper or a white piece of cloth to avoid staining his hands with blood, and proceeded to make a cut in his abdomen from left to right. As soon as that occurred the kaishakunin (assistant) would perform the daki-kubi to avoid the person unnecessary pain.
There is also a seppuku imposed as a capital punishment for criminals or disgraced samurai. They had a determinate span of time to commit seppuku or they would be decapitated. This act would not release their families from being dishonored, though.
Women would also commit seppuku, but its procedure is different: they would tie their ankles to avoid falling to the ground with their legs spread (something considered disgraceful). Though the reasons for this procedure have the same motivations as a seppuku, it is described as a 'regular' suicide in Japanese: jigai.