Short-barreled rifle is a legal designation in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, referring to a shoulder-fired, rifle

Rifle

A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

d firearm with a barrel length of less than 16 inches (40.6 cm) or overall length of less than 26 inches (66.0 cm). In the United States, an SBR is an item regulated by the Bureau of Alcohol, Tobacco, Firearms and Explosives

Bureau of Alcohol, Tobacco, Firearms and Explosives

The Bureau of Alcohol, Tobacco, Firearms and Explosives is a federal law enforcement organization within the United States Department of Justice...

 (BATFE) as an NFA firearm. In the absence of local laws prohibiting ownership, American civilians may own an SBR provided it is registered with the BATFE, and a $200 tax is paid prior to taking possession of or creating the firearm.
Overall length is measured between the extreme ends of the gun, along a centerline which passes through the middle of the barrel.