MOA (Minute of Angle)
Also known as: minute of angle
An angular measurement equal to 1/60th of a degree — about 1.047 inches at 100 yards — used for scope adjustments and group sizes.
A minute of angle is 1/60th of one degree of arc. Because it's an angle, the distance it covers grows with range: roughly 1.047 inches at 100 yards, ~2.09 inches at 200, ~3.14 inches at 300, and so on. Shooters round it to '1 inch at 100 yards' for quick mental math. Most hunting and target scopes adjust in 1/4-MOA clicks, meaning each click moves your point of impact about a quarter inch at 100 yards.
MOA is used two ways: to describe how precise a rifle is ('a sub-MOA rifle' groups under ~1 inch at 100 yards) and to make sight corrections. If your group is 2 inches low at 100 yards, that's about 2 MOA, or 8 clicks up on a 1/4-MOA turret. Knowing MOA lets you translate what you see on paper into exact turret adjustments.