A measure of length (or distance) in US units.
This ruler (not to scale) measures up to 12 inches, or up to 30 centimeters along the bottom.
There are 12 inches in a foot, and 36 inches in a yard.
The abbreviation is: in
Or sometimes the double quote mark: "
Example: 16 inches can be written 16 in, or just 16"
One inch is exactly 2.54 centimeters.
See: Centimeter