“of the Philistine.” After killing Goliath in the Valley of Elah, the Israelite army chased the Philistines all the way to Gath. During that time, word of David’s victory over Goliath spread, and so when David and Saul returned to Gibeah, the women came out and sang and danced.
“musical instruments.” The Hebrew word is related to the word “three,” so this word may be referring to a specific instrument that has three strings, or a triangle with three sides.