There is a lot of talk these days about the definition of leather.
Legal Definition, BS 2780 (1983) Definition
In the UK a definition of leather is set out in the British Standard Glossary of Leather Terms (BS 2780) and this definition is used as a guide in applying consumer protection legislation such as the Sale of Goods Act and the Trade Descriptions Act. the definition, which is by far the most commonly cited in the world, says Leather is:
Hide or skin with its original fibrous structure more or less intact, tanned to be imputrescible. The hair or wool may or may not have been removed. It is also made from a hide or skin that has been split into layers or segmented either before or after tanning.
Note 1: If the leather has a surface coating, the mean thickness of this surface layer, however applied, has to be 0.15mm or less.
Note 2: If the tanned hide or skin is disintegrated mechanically and/or chemically into fibrous particles, small pieces or powder and then, with or without combination of a binding agent, is made into sheets or forms, such sheets are not leather.
I wrote about the Brazilian Leather Law (1965, the Leather Law (nº 4.888)) back in 2013, but it is worth adding this visual to help us understand what it is all about.