Caliber is a kind of measurement that can describe either the level of a person’s ability or the diameter of a gun barrel. Your dad might be a high-caliber marksman, especially when using his .22 caliber rifle.
Caliber describes the level of ability a person has achieved in a profession. For example, you probably wouldn't want to hire a low-caliber plumber when the toilet breaks. The caliber of an institution or a program describes the height of its standards. You might be planning to attend the high-caliber veterinary program at your state university. Caliber is also the measurement of the width inside a gun barrel, and its corresponding bullets.