A bobbin is the part of a sewing machine on which the lower thread is wound. The machine makes a stitch by catching the bottom thread, from the bobbin, with the top thread, from the needle.
Most bobbins are wound with thread and inserted in sewing machines, but the word describes many spools and cylinders that hold string, yarn, wire, or other materials. Some machines contain bobbins, wound with wire or tape, and a weaver or knitter often works with a yarn bobbin close at hand. Bobbin comes from the French bobine, "small instrument used in sewing," which shares a Latin root with babble, for the sound it makes while unspooling.