The number a character needed to roll on a d20 to hit a target of Armor Class 0; subtract the target's AC to find the roll needed against anything else. It compressed pages of attack tables into one value, but its double negatives became a byword for clunky rules. It was retired when third edition introduced ascending AC in 2000.
Origin
Implicit in the combat matrices of AD&D's 1979 Dungeon Masters Guide; it became the core attack rule of AD&D 2nd Edition (1989).
Quick answers
- What does "THAC0" mean?
- The number a character needed to roll on a d20 to hit a target of Armor Class 0; subtract the target's AC to find the roll needed against anything else. It compressed pages of attack tables into one value, but its double negatives became a byword for clunky rules. It was retired when third edition introduced ascending AC in 2000.
- Where does the term "THAC0" come from?
- Implicit in the combat matrices of AD&D's 1979 Dungeon Masters Guide; it became the core attack rule of AD&D 2nd Edition (1989).