Fat Quarter is a common sewing/quilting term. It means 1/4 of a one yard piece of fabric, Cut as if you cut that piece of fabric in half each way into four like-sized pieces. Thus, 36" x 45" wide fabric would equal 4 "Fat Quaters", each approx. 18" by 22 ". The exact measurements may vary slightly based on the width of the fabric. That's why I also include the measurements of each piece of fabric I have listed.