a piece of a butchered animal: one of the sections a carcass is cut into at the joints
A netach is one of the sections a butchered animal is divided into. It is not a fragment or a scrap. It is a part separated deliberately, the way a butcher takes the thigh off at the joint and sets the shoulder beside it. The word belongs with the verb "to cut up" (נָתַח), which stands next to it in almost every verse: the animal is cut into its pieces, and the pieces are then what someone handles. Hebrew has a different word for an animal split in half down the middle for a covenant ceremony (בֶּתֶר); this one is about jointing a body into its several parts.
Most often the pieces are the parts of an animal being offered up whole. The instructions are unhurried and physical: skin the animal, cut it into its pieces, wash what needs washing, then lay the pieces with the head and the fat on the wood over the fire. Counting the pieces and setting them in order is part of the offering itself, not merely getting ready for it. The word almost always shows up as a set of pieces rather than a single one, because the point is a whole body accounted for part by part.
Away from the altar the same word names cuts of meat for a pot, and once the parts of a human body. In Ezekiel's picture of a boiling cauldron, the choice pieces of thigh and shoulder are the people of Jerusalem, thrown in and later dragged out one by one. In Judges the man who cuts his dead concubine into twelve pieces is described in the vocabulary of the slaughtering floor, and that is exactly the horror: a person handled like a carcass. "Pieces" reads flat in English there, while the Hebrew word never loses the knife.