Defense is a value found on armor and characters as well as traits. Defense and attack directly influence turn power during combat. For more information on the exact manner in which Defense influences combat see the mechanics article.
Players gain bonus defense based on their level. The amount is equal to the player's level divided by five, rounded down. That is, at fifth level, the player has one bonus defense, and a tenth level player will have two bonus defense. This appears as a green "+#" entry on the set-up description on the Camp page following the Defense Power of the armor currently equipped.