Point-blank range
The sights of a gun are set so that the barrel has a small upward tilt. When the bullet leaves the gun, it starts by rising and later drops. This means that weapon hits too low for very close targets, too high for mid-range targets, too low for very far targets. It hits point blank at the two distances when it crosses between too low and too high.  For a .270 Winchester, as an example, the bullet first crosses the line of sight at about 23m (25 yds) as it is rising and again at about 250m (275 yds). With this gun, point blank range for a deer size target is about 275m (300-310 yards).