Yarn dyed fabric or fabric that uses thread that has been dyed before they weave it into fabric tends to hold it's color better and the fabrics raw edges are the same color. piece dyed or fabric that is woven with white yarn or untreated yarn sometimes is colored on one side and white on the other yarn dyed fabric will be the same on both sides
yarn dyed fabrics are those that have more than one color such as gingham, plaid, stripes etc. while piece dyed ones are primarily one solid color.