The Priority of Life Code is a SRU/Toronto Police Force code that all officers must adhere to. Basically it states that these individual's lives are important:
1) Life of the Hostage
2) Life of the police officer(s)
3) Life of the Hostage Taker(s)
In threat situations, the code is reversed.
1) Deal with the Hostage Taker first
2) Rescue affiliated people/family members
It is because of the Priority of Life code that Jules did not want to form a relationship with Sam Braddock. Dr. Toth and Jules recount the code during Toth's polygraph analysis in Episode:Fault Lines. In the episode, Episode:Priority of Life, Sam follows the code, saving the injured hostage first, then Jules. In Episode:Keep The Peace, Part I, Ed Lane tells Donna Sabine to follow the reverse code, tackling Anson Holt first than saving Ed's son, Clark Lane.