Bullet Drop
How far the bullet falls below the line of sight at a given distance. Measured in inches, mils, or MOA depending on context.
A 6.5 Creedmoor with a 100-yard zero drops about 8 mils (28 MOA) at 1,000 yards. The shooter compensates by dialing or holding elevation to lift the muzzle so the descending bullet meets the target.
Drop is predictable once you feed the math good inputs. Most modern ballistic apps will print a drop chart accurate within a click or two of dialing if you give them honest muzzle velocity, BC, and atmospherics.