From Wikipedia:
Some females belonging to
samurai families committed suicide by cutting the
jugular vein with a knife such as a
tantō or
kaiken. The main purpose was to achieve a quick and certain death in order to avoid capture. Before committing suicide, a woman would often tie her knees together so her body would be found in a dignified pose, despite the convulsions of death.
Jigai, however, does not refer exclusively to this particular mode of suicide. Jigai was often done to preserve one's honor if a military defeat was imminent, so as to prevent
rape. Invading armies would often enter homes to find the lady of the house seated alone, facing away from the door. On approaching her, they would find that she had ended her life long before they reached her.