A sticky note is a small piece of paper with a strip of glue along one edge that make it "sticky," so you can stick it to things.
The most common sticky note is the Post-It, which is made by a company called 3M. In 1974 a man named Arthur Fry came up with the idea for the sticky note. He used a glue that was originally too weak to be used for anything else, so the notes would come off easy. 3M started to sell Post-Its in 1980.