Good question. These are precut pieces of fabric that are bundled together and sold at quilt shops. Moda fabrics has trademarked these terms.
Charm pack = a bundle of different 4" or 5" squares from the same line, all coordinating fabrics
Jelly roll = a bundle of different 2.5" strips, rolled together.
Turn over = a bundle of different triangles.
Layer cake = 10" squares, bundled together
Sometimes when quilters make a scrappy quilt or a sampler they like these bundles as they are already coordinated and cut.
They tend to be somewhat pricey, because more labor has been involved in getting these to the store.