Fabric charms are small pieces of material that are swapped or shared by quiltmakers. Typically cut in squares, they can be of any size, though inch increments are usually used and the size is rarely above 10 inches. A quiltmaker will usually choose one size and collect many charm squares of that size.
For example, I have thousands of 3-inch charms and even more 5-inch charms. Why? Hard to say. Collecting charms is a hobby, distinct from sewing or quilting. Someday I may make a charm quilt with them. Or maybe not.
In the years leading up to 2000, quiltmakers started a charm-square mania, swapping small bits of fabric with people in every state of the United States or from every country in the world. Quilts made of this collection are called millennium quilts and often have exactly 2000 pieces.