Health or vitality is an attribute assigned to entities such as characters or objects within tabletop role-playing games and video games, that indicates their continued ability to function while damaged or injured. Health is usually measured in hit points or health points, shortened to HP which lowers by set amounts when the entity is attacked or injured. When the HP of a player character or non-player character reaches zero, that character is considered either dead or incapacitated and barred from taking further action. In single player games, running out of health usually equates to "dying" and losing a life or receiving a Game Over. In some games, such as those with cooperative multiplayer, it is possible for an ally to revive a character who has reached zero HP. Any entity within a game could have a health value, including the player character, non-player characters, and objects. Indestructible entities have no diminishable health value. Health might be displayed as a numeric value, such as "50/100". Here, the first number indicates the current amount of HP an entity has, and the second number indicates the entity's maximum HP. In video games, health can also be displayed graphically, such as with a bar that empties itself when an entity loses health, icons that are "chipped away", or in more novel ways.
Dungeons & Dragons co-creator Dave Arneson described the origin of hit points in a 2002 interview. When Arneson was adapting the medieval wargameChainmail to a fantasy setting – a process that, with Gary Gygax, would lead to Dungeons & Dragons – he saw that the emphasis of the gameplay was moving from large armies to small groups of heroes and eventually to the identification of one player and one character that is essential to role-playing as it was originally conceived. Players became attached to their heroes and did not want them to die every time they lost a die roll. Players were thus given multiple hit points which were incrementally decreased as they took damage. Arneson took the concept, along with armor class, from a set of a naval American Civil War game's rules. The US Navy used a similar concept in their tactical war games already in 1920s and 1930s. In their simulation, each ship had a "life" parameter. The unit of Life of the ship was a number of "equivalent penetrative 14-inch shell hits". The Navy considered, e.g., that a Kongō-class battlecruiser had 12 Life points and a Nagato-class battleship had 18.8. A visual power meter representing stamina was used in Nintendo's 1983 arcade game Punch-Out!!
In action video games as well as in role-playing games, health points can usually be depleted by attacking the entity. A defense attribute might reduce the amount of HP that is lost when a character is damaged. It is common in role-playing games for a character's maximum health and defense attributes to be gradually raised as the character levels up. In game design, it is deemed important that a player is aware of it when they are losing health, each hit playing a clear sound effect. Author Scott Rogers states that "health should deplete in an obvious manner, because with every hit, a player is closer to losing their life." The display of health also helps to dramatize the near-loss of a life.
Player characters can often restore their health points by consuming certain items, such as health potions, food or first-aid kits. Staying a night at an inn fully restores a character's health in many role-playing video games. In general, the different methods of regenerating health has its uses in a particular genre. In action games, this method is very quick, whereas role-playing games feature slower paced methods to match the gameplay and realism. Some video games feature automatically regenerating health, where lost health points are regained over time. This can be useful to not "cripple" the player, allowing them to continue even after losing a lot of health. However, automatically regenerating health may also cause a player to "power through" sections they might otherwise have had to approach cautiously simply because there are no lasting consequences to losing a large amount of health. To strike a balance between these extremes, many games have implemented a hybrid system, whereby the player only automatically regenerates health to a certain point; they must seek other means to restore the rest. This mechanic initially appeared in action role-playing games, with early examples including the Hydlide series, the Ys series, and Woody Poco. In Woody Poco, the rate at which health recharges is based on food level. In Hydlide and Ys, the player character has to stand still for their health to automatically regenerate. This system was popularized in first-person shooters by , though regenerating health in The Getaway has been cited to be more comparable to later use of the mechanic in first-person shooters.
The way health is displayed on the screen has an effect on the player. Many games only show the health of the player character, while keeping the health of enemies hidden. This is done in the Legend of Zelda series, Minecraft and Monster Hunter series to keep the player's progress in defeating their enemy unclear. In these games, the fact that the enemies are being damaged is indicated by their behavior. On the other hand, many fighting games, such as the Street Fighter series, use easy-to-read health bars to clearly indicate the progress the player is making with each hit. It is common in first-person shooters to indicate low health of the player character by blood spatters or by a distorted red hue on the screen, attempting to mimic the effects of wounding and trauma. These visual effects fade as health regenerates.