Umbrella term for the special operations troops in a military, typically those with better training and equipment, and who perform higher-risk and more secretive missions.
In US context, it applies specifically to the US Army's SF group, known to the public as the Green Berets, who specialize in behind-the-lines operations such as hit-and-run tactics, intelligence gathering and moreover, gathering the support of locals to train and support militias for counter-insurgency purposes.
As a US-specific umbrella term, it also applies to the Army Rangers (of which the late football star
Pat Tillman was with), the Air Forces
Pararescue Jumpers (PJ's for short), the iconic Navy SEALs, and the
Force Recon Marines, who for all intents and purposes do the same job as the aforementioned SEALs.