Ream - What does ream mean?

Definition of REAM:

A standard unit of measure relating to paper quantity. Internationally, a standard ream is defined as 500 sheets of paper that are of the same size and quality. Historically, the number of sheets in a ream has varied, usually depending on the size and quality of the paper; examples include the Mill Ream (472 sheets), Stationer's Ream (504 sheets), Printer's Ream (516 sheet), and a ream of 480 sheets - today known as a Short Ream compared to 500 sheets, which is known as a Long Ream. Some specialist papers are still sold in these alternative measures.