Post-it note

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 unique 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 now available in a wide range of colors, shapes and sizes.

Although 3M's patent ran out in 1997, "Post-it" and the original notes' distinctive yellow color remain registered company trademarks, with terms such as "repositionable notes" used for similar offerings manufactured by competitors. Despite this, the name has become genericized for all such products in many countries.

https://en.wikipedia.org/wiki/Post-it_note