Creases are a type of wrinkle or fold in fabric that can be caused by a variety of factors. LINES, folds, rucks, and seams are all types of creases. LINES are thin, straight wrinkles that can be caused by folding or pressing fabric. Folds are thicker, more pronounced wrinkles that are created when fabric is bent or folded. Rucks are small, tight wrinkles that are caused by gathering or pleating fabric. Seams are the LINES created when two pieces of fabric are sewn together.