Minute of Angle
Minute of angle (MOA) is the measurement(in fractions of degrees) of a ballistic round's deviation from its inital heading due to gravity and/or the effect of air resistance on velocity.Informally known as a "Bullet's Trajectory" or "the rainbow effect". Long range weapons must account for this effect because a fired round falls at an exponential rate Weapons such as large caliber rifles use scopes with adjustments for distance and windage.