Seppuku (切腹, 'cutting [the] belly'), also called harakiri (腹切り, lit. 'abdomen/belly cutting', a native Japanese kun reading), is a form of Japanese ritual suicide by disembowelment. It is done by plunging a short blade (such as a tanto) into the belly and slicing open the abdomen horizontally. If the cut is deep enough, it can sever the abdominal aorta, causing death in mere seconds by rapid exsanguination... if not, the victim could remain alive for hours of ongoing agony. For this reason, a kaishakunin (Japanese: 介錯人) is often appointed to behead the victim at the moment they gut themselves, sparing them from prolonged suffering.
Seppuku was originally specifically intended for samurai as a part of their code of honour - typically, dishonored samurai were ordered to commit seppuku as a form of capital punishment. However, it has also been done voluntarily by other Japanese people - particularly, military officers near the end of World War II. Seppuku was considered the most honourable capital punishment apportioned to samurai, so to restore honour for themselves or for their families a disgraced samurai could request the right to perform seppuku instead of being executed in another, less honorable way. It was also done voluntarily by defeated samurai so they could die with honour rather than fall into the hands of their enemies.