A fat quarter is a pre-cut piece of fabric. Most fabric shop have a large box full of colorful fabric so you can mix and match. You don't have to carry bolts up to get cut.
My Walmart, who got rid of their fabric department, still sells fat quarters, jelly rolls (2 1/2" strips of different, but coordinating fabric), and some charms (4" sq. package of coordinating fabric),I think.
I hope I am explaining this clearly