Blood innocence is the state in which one is innocent and pure from violence, or rather, one who has not shed blood. A notable example of this was Gabrielle, who preserved her blood innocence early throughout Xena: Warrior Princess until The Deliverer, wherein she accidentally killed the priestess Meridian of Dahak's Cult.
Often times, one may feel distraught and immense guilt following their first kill. One may also fall into depression due to the lost of their blood innocence; this in turn may also impact one's life very much. It became one of many catalysts that led to Gabrielle's upbringing as a full-fledged warrior, and Joxer's maturing following his first kill in The Convert.
Blood innocence was also a significant component to Dahak's coming. The lost of one's blood innocence made it possible for Dahak to impregnate Gabrielle, who eventually gave birth to the Bringer of Evil, Hope. This is also one of the reasons why the Rift occurred.