a fleece: the woolly coat cut off a sheep in one piece and handled as a single object.
This word names one thing, and names it narrowly: wool that has been shorn from a sheep and stays together as a mat. It is formed from the ordinary verb for shearing (גָּזַז), so it always points to wool already off the animal, heavy enough to pick up, spread out, and wring out by hand.
Its whole use in the Bible sits inside one short scene. Gideon asks God for a sign, lays a fleece on the threshing floor overnight, and asks first for dew on the wool with dry ground all around it, then for the opposite. The word turns up seven times in those four verses and nowhere else in the Bible.
The first time it appears, the story spells it out as "a fleece of wool," pairing it with the usual word for wool as a material (צֶמֶר); after that it is simply "the fleece," an object the reader already knows. Hebrew has a second word from the same root (גֵּז) that can mean a shearing of wool but can equally mean a mowing of grass. The word here is the narrower one: it never means anything but the sheep's fleece.