There are two varieties of armor found in Doom: Green (Standard) armor, and Blue (Mega) armor. Blue absorbs more damage than green. Armor bonuses have the same armor class as a suit of Green armor. Absorbing damage, in this case, means that a certain percentage of damage dealt to the player is removed from the amount of armor the player has and the player's health is spared the expense. In the case of green armor, that percentage is 33, and blue armor spares the player 50% of the total damage of an attack.
Heretic has its own armor and armor classes. Heretic's silver shield protects the player from 50% of damage, while the enchanted shield protects the player from 75%.
Hexen has even broader and more complicated types of armor and armor classes, which are out of the scope of this article.