Real Dictionary

paper
uncountable noun: Paper is a material that you write on or wrap things with. The pages of this book are made of paper.

paper in American English
a thin, flexible material made usually in sheets from a pulp prepared from rags, wood, or other fibrous material, and used for writing or printing on, for packaging, as structural material, as a fabric substitute, etc.
noun: a substance made from wood pulp, rags, straw, or other fibrous material, usually in thin sheets, used to bear writing or printing, for wrapping things, etc.

paper in British English
noun: a substance made from cellulose fibres derived from rags, wood, etc, often with other additives, and formed into flat thin sheets suitable for writing on, decorating walls, wrapping, etc