HP

HP stands for Hit Points. They determine a character's staying power against obstacles which harm you, and when you hit zero the character is rendered useless under most circumstances. Hit points are notoriously abstract in that they don't have a direct representation in the real world - that is, there is no IRL system of categorizing wounds equivalent to varying amounts of HP damage.

In D&D 0 HP means that a character is unconscious and -10 means that a character is dead. A character on 0 or below may be bleeding out or otherwise slowly dying.