what is the difference between a pin and a brooch?

A pin is a device used to fasten materials together.  For example, Victorian Bar Pins were used to help hold a lady's collar together and worn at the top of the neck.  A brooch is a decorative jewelry item. A brooch usually has a connotation of being a larger vintage estate piece. A brooch sometimes can be used as a pendant or to hold a scarf or piece of clothing.