Others have tended to use 'parchment' as a generic term for all products except those made from calfskin, for which they reserve the term 'vellum'. Authorities in the field aren't quite as dogmatic in their approach. Furthermore, he argues that the word 'vellum' may actually derive from the latin 'pellis', simply meaning 'skin'. The impression I get is that in academic circles, this controversy over the usage of the two terms is regarded as rather tedious, and I tend to agree. My impression is that conservators and codicologists tend to use the term 'parchment' generically, and avoid the term 'vellum' since it seems to mean different things to different people.
Parchment is by no means a uniform product.
There is considerable latitude in how a skin can be converted into parchment. Considering the many variations on the manufacturing process that have been used over the centuries, and in different places, any rigid categorization based on the method of manufacture is of questionable validity. While some variations in the procedure may only lead to subtle differences in the finished product, others can yield differences that are quite marked. My own feeling is that, the differences between animal species aside, there are two broad categories of parchment. On the one hand are parchments that might be termed 'Full-grain', where the grain layer has been left more or less intact on the hair side.