I have come across a similar degree of confusion on another forum. Apparently, "bobbin" doesn't translate quite correctly into many languages. A bobbin is a form on which you can wind something. For example, a bobbin for thread is a small cylinder of wood or plastic on which sewing thread can be wound. In electronics, it is usually a plastic form on which wire is wound as in a transformer.
Here are a couple of examples of bobbins that are designed to fit sewing machines, but many people also use them for hobbiest electronic projects:
Plastic sewing bobbins: