The Collaborative International Dictionary of English v.0.48:

SWAT team \SWAT" team`\, Swat team \Swat" team`\(sw[o^]t"
   t[=e]m), n. [acronym: Special Weapons and Training.]
   a special group of police trained to deal with unusually
   dangerous or violent situations, and having special weapons,
   such as rifles more powerful than those carried by regular
   police officers. They are employed, for example, in
   situations when hostages are being held, or heavily armed
   persons need to be captured. Called also SWAT or
   S.W.A.T..

WordNet (r) 3.0 (2006):

SWAT team
    n 1: a squad of policemen who have been trained to deal with
         violent and dangerous situations [syn: SWAT team, SWAT
         squad, Special Weapons and Tactics team, Special
         Weapons and Tactics squad]