The term 'sewing machine spool' refers to a BOBBIN, which is a small cylindrical object that holds thread or yarn. It is used in sewing machines to store the thread and feed it through the machine as needed. The BOBBIN is usually made of plastic or metal and is placed inside the machine's BOBBIN case. The BOBBIN is an essential part of the sewing machine, as it helps to keep the thread in place and allows the machine to sew properly.