"Green Beret" is the commonly used term for the United States Army Special Forces (SF).
The unit is led by the lieutenant General of the United States Army Special Operations Command. First organized under the 10th Special Forces Group, which also included the US Army Rangers, it was officially recognized by President Kennedy in 1961.
The Green Beret reference comes from the unit's distinctive headgear, authorized by President Kennedy. The Green Berets are tasked with duties that include direct action, strategic reconnaissance, and the training of allied forces at war.