HP, or "Hit Points", are very important character statistic and play a very large role in the Fire Emblem universe. The term is used in several other video games and usually plays the same role. HP appears as a green bar at the bottom of the screen during a fight. However, if the animations are turned off, the HP bar will often be a different color for unknown reasons. It can be depleted by damage, but if the Defense of your unit is higher than the enemy's Attack and vice versa, No Damage will pop up upon the hit and a distinctive tink sound can be heard. HP has a higher stat cap than the other stats, but units also have higher growth rates for it.
All characters start with a certain amount of HP. Some classes, such as the Knight and the Fighter, customarily have more HP than most units, whereas the Archer and Mage usually have less. Damage will remove a certain amount of HP from the unit taking damage, and when a character has 0 HP left they will die, or retreat from the battle if they are important to the storyline. Units with more than 80 hitpoints will have their hitpoints bar changed to a purplish color with "??" shown as the amount of their health to add suspense into the battle. This usually applies to endgame bosses in those series, although in The Sacred Stones, Cyclopses can have over 80 hitpoints.
Recovery Items always have the same general effect; to recover lost HP. Many Staves also recover lost HP. Some buildings and structures (ex. fortresses, thrones, gates...etc.) may recover small amounts of the HP if the unit standing upon it finishes his/her turn there. Certain weapons, like the tome Nosferatu and the dark magic infused Runesword, among others, do not only remove HP from the attacked unit, but also heal the attacker, who then receives the same number of HP. In some games, there are also skills like Renewal and Imbue which heal the character when certain conditions are met.