In Dungeons & Dragons (D&D), "AC" stands for Armor Class. This is a key number you'll see on your character sheet, and it plays a crucial role during the game, especially in combat. Think of AC as a representation of how hard it is to land a hit on your character with a physical attack. The higher your Armor Class, the more difficult you are to hit.

Here's a simple breakdown of how it works: When someone or something tries to hit your character with a physical attack, they roll a 20-sided die (a d20) and add any relevant bonuses they have to that roll. They're aiming to match or exceed your AC. If their total equals or surpasses your Armor Class, they've managed to hit you, and you'll likely take damage. If they don't reach your AC, their attack misses, and your character avoids the damage.

Your Armor Class is determined by what your character is wearing (like armor or magical protections), their Dexterity modifier (reflecting agility and reflexes), and any other bonuses from class abilities, spells, or equipment. For example, wearing heavy armor will give you a high AC because it's tough and protective, but it might limit your mobility. On the other hand, a character who relies on speed and agility might have a lower AC but is harder to hit because they can dodge attacks.

Understanding and managing your AC is vital for surviving in D&D. It influences the gear you might seek out, the spells you consider, and how you position yourself in battle. Always know your AC and think about ways to improve it to help your character last longer in fights.