The term assault weapon is used in the United States to define different types of firearms. The definition varies among regulating jurisdictions, but usually includes semi-automatic firearms with a detachable magazine, a pistol grip, and sometimes other features, such as a vertical forward grip, flash suppressor, or barrel shroud. Certain firearms are specified by name in some laws that restrict assault weapons. When the now-defunct Federal Assault Weapons Ban was passed in 1994, the U.S. Department of Justice said, “In general, assault weapons are semiautomatic firearms with a large magazine of ammunition that were designed and configured for rapid fire and combat use.” The commonly used definitions of assault weapons are under frequent debate, and have changed over time.
The origin of the term has been attributed to legislators, the firearms industry, gun control groups, and the media. It is often used interchangeably with the term “assault rifle“, which traditionally refers to selective fire rifles that use intermediate cartridges. After the December 2012 Sandy Hook Elementary School shooting, many news organizations ran stories about assault weapons, explaining their varying definitions and presenting varying opinions about whether they should be banned again at the federal level. (Source)