The world of Ivalice is ruled by Law and Order. All battles are adjudicated by "Judges" who are there to help enforce the constantly changing "World Laws". The current "World Laws" can be viewed by; pressing L on the World Map screen, pressing Select during Battle formation, and by selecting the "World Law" option from the System Menu during a battle.
If a unit breaks a law in combat, the Judge will give that unit a Yellow "Caution" Card, which will mean that unit will be penalised at the end of battle. Also, if that unit continues to break the law or breaks the law to defeat a unit, the Judge might give that unit a Red "Arrest" Card; which will mean that unit will be sent to a nearby Prison. You must pay a lot of Gil to either "Bail" the jailed unit out of Prison, or to "Acquit" them to remove any cards.
Judges also award JP (Judge Points) to units that legally defeat their enemies. With JP you can use strong Combo attacks, and if you gain the maximum amount (10) you can summon the powerful "Totemas". Judges will also move "unconscious" units out of the way to keep the battle flowing. Later in the game it will be possible for you to add and remove laws by using "Law Cards".