Hit points, sometimes abbreviated as HP, is the basic unit of health in the Stamina modes of Super Smash Bros. Melee, Brawl, Super Smash Bros. for Wii U, and Super Smash Bros. Ultimate. It has since also been used the unit of health for bosses, and for enemies in Adventure Mode, the Subspace Emissary, and Smash Run. When a character is hit by an opponent's attack, their hit points decrease. The character can continue as normal until their hit points are reduced to 0, when they are KO'd. The health of two recurring bosses in the Super Smash Bros. series, Master Hand and Crazy Hand, are always measured in hit points, unless otherwise altered by the Master Hand glitch or an Action Replay.
Hit points of a character decrease just like damage is raised, so if an attack did 10%, it would decrease the opponent's HP by 10 points. Once the HP reaches 0, the character (or boss) will show an animation sequence of that character fainting, during which the sequence the other characters move in slow motion. In the case of Adventure mode enemies, when their HP is reduced to 0, they will be sent flying back until they pass a blast line or disappear.
In terms of game coding, HP in Stamina battles is equal to a negative damage value — that is, an HP displaying as 123 HP is actually a damage of -123%. This explains why characters take minimal knockback in stamina matches until they are defeated (HP drops to 0, knockback begins to rise above 0%). In the same way that damage is displayed as an integer but tracked as a decimal (so a damage of 14.6% is reported as 14%), HP is also rounded down — although as it is considered negative, it is rounded up (using the floor function in math), so a value of 14.6 HP would be displayed as 15 HP; this has the side effect of any HP value between 0 and 1 (such as 0.4) being reported as 1, so it is impossible to display a 0 if the character is not defeated. However, decimal HP is displayed in Ultimate. On the other hand, HP for enemies and bosses (at least in Brawl) is a positive number that is decreased on taking damage.