A charm quilt is a one-patch quilt using a different fabric for every piece. No repeats allowed. Some charm quilts have over a thousand different fabrics in them.
Usually a quilt made using only one shape, such as a triangle or hexagon, where every single shape is a different piece of fabric. No fabric is repeated in the quilt.
A quilt made of many, many small patches (traditionally 2" or so) where each piece is a different fabric. The pattern is usually a one-patch design and often involves swaps and trades with friends to gather many fabrics.