A ritual suicide practiced by samurai in Japan, usually because he has brought shame and dishonor to himself. This might have resulted from failing to protect his master, or otherwise breaking the code of bushido, "the way of the warrior". The soon-to-be-deceased kneels with a short sword in both hands, and disembowels himself. Immediately after this, the sepuku assisant, known as the kaishakunin or "second", beheads the person with a sword. The ritual goes into great detail about washing and dressing, last words, etc.
The disgraced samurai was asked to commit sepuku by his superiors.