An artists tool used in the drawing process. It is also often reffered to as a 'rubber'. Generally speaking an eraser is any material that can remove lines or marks in artwork. This usually applies to pencil or charcoal lines drawn on paper.
There are 3 main types of erasers that artists use:
Plastic Eraser: Useful for general pencil erasing and cleaning surfaces. Particularly good for keeping a clean paper surface, so this one is preferred for artists using fine drawn detail using graphic pencils. More: Plastic Eraser.
Art Gum Eraser: A semi-transparent or light brown color gum eraser. It tends to produce a lot of ‘crumbs’ and can be considered the least useful of the 3 main types of erasers. More: Gum Eraser.
Kneaded Eraser or Putty Rubber: The best and most useful type of eraser if you are learning how to draw with several drawing mediums. It can be kneaded between the fingers to provide a clean surface and specific shape for erasing small spaces. More: Putty Rubber.