A Post-it Note (or sticky note) is a small piece of paper with a re-adherable strip of glue on its back, made for temporarily attaching notes to documents and other surfaces. A low-tack pressure-sensitive adhesive allows the notes to be easily attached, removed and even re-posted elsewhere without leaving residue. Originally small yellow squares, Post-it Notes and related products are available in various colors, shapes, sizes and adhesive strengths. As of 2019, there are at least 26 documented colors of Post-it Notes.