What is abrasive paper and what is it used for?

Abrasive paper is also called emery paper or "sand" paper.

It a sheet of strong paper onto which some glue is pasted on one side and into this wet clue particles of sand (or other rough material) are stuck.

Once the glue dries, the rough side of the paper can be used to rub (and smooth) an object (or file your nails).