From BiblePortal Wikipedia

Easton's Bible Dictionary [1]

 Joshua 13:3 2 Samuel 6:10

Holman Bible Dictionary [2]

 Joshua 13:3Gath

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [3]

(Heb. Gitti', גַּתַּי ; Sept. Γεθαῖος ), an inhabitant or native properly of the Philistine city GATH ( Joshua 13:3). Obed-Edom, in whose house the ark was for a time placed ( 2 Samuel 6:10), and who afterwards served in Jerusalem ( 1 Chronicles 16:38), although a Levite ( 1 Chronicles 26:4), is called a Gittite ( 2 Samuel 6:10), possibly because he had been with David when at Gath, but much more probably from his being a native of Gath-Rimmon which was a city of that family of the Levites to which he belonged ( Joshua 21:24). There seems to be no reason for extending this interpretation to Ittai ( 2 Samuel 15:19), seeing that David expressly calls him "a stranger" (foreigner), and, what is more "an exile." He was at the head of 600 men, who were also Gittites, for they are called ( 2 Samuel 15:20) his "brethren." They appear to have formed a foreign troop of experienced warriors, chiefly from Gath, in the pay and service of David, which they had perhaps entered in the first instance for the sake of sharing in the booty obtainable in his wars. (See Cherethite).