The term "speciesism" has become in common use, both in current language and in the literature for the protection of animals. However, with a careful analysis of the variety of definitions offered in many dictionaries and encyclopedias of the sector, it emerges that its meaning is not always univocal. This neologism thus appears to be both indispensable and ambiguous. To make it clearer, I propose to study its genesis and historical development. The word speciesism was invented by the psychologist Thomas Ryder in the early Seventies of the last century, in the context of the Oxford Group and was later philosophically accredited by Peter Singer. Its value varies from being a psychological expedient useful to ask questions about the opportuni...