Hit points (sometimes abbreviated "hp") represent two things in the game world: the ability to take physical punishment and keep going, and the ability to turn a serious blow into a graze or near miss. As you become more experienced, you become more adept at parrying strikes, dodging attacks, and rolling with blows such that you minimize or avoid significant physical trauma, but all this effort slowly wears you down. Rather than trying to keep track of the difference between attacks and how much physical injury you take, hit points are an abstract measure of your total ability to survive damage. ...
Over the years, some players have developed a terrible misconception that a character with 100 hit points can be shot almost a dozen times in the chest. Not true! Both a high-level soldier with 100 hit points and a stormtrooper with 10 hit points will be grievously injured and possibly killed by a single blaster wound to the chest. However, the high-level soldier will dodge the first nine shots, and the stormtrooper won't. (If it helps, imagine that a high-level hero has a reserve of "virtual hit points" to offset attacks that would otherwise be lethal. Once he has exhausted his reserve, the blow that finally reduces him to 0 hit points will solidly connect and cause serious physical trauma.)