Quilt or quilted maple refers to a type of "figure" in maple wood. It is seen on the tangential plane (flat-sawn) and looks like a wavy "quilted" pattern, often similar to ripples on water. It is a distortion of the grain pattern itself. Prized for its beauty, it is used frequently in the manufacturing of musical instruments especially guitars. Quilted maple is an end grain figure that shows a circular pattern on flat sawn material. There are many terms that describe the shape and pattern of quilted maple. Aka watered, popcorn, tubular, sausage, bubble wrap, angle step.
High quality (3A grade or above) quilted maple can be extremely expensive. A standard guitar billet made of 5A (premium) quilted maple costs a few hundred dollars.