Random or felted sheet of isolated vegetable fibre produced by sieving the macerated vegetable fibre from a watery slurry. Certain criteria must be met for a substance to be called paper: most importantly, the fibre must be vegetable; it must be processed in some way to break the material into individual fibres; and the sheets must be formed by casting the macerated fibre–water mixture on a sieve, usually a screen that is dipped into the aqueous mixture and allows the excess water to drain away. Paper is the most common support for drawing, printing, prints, watercolour painting and writing; with parchment, it was also widely used for the medieval manuscript, and for the development, from the 15th century onwards, of the printed book.