Natural kinds

Natural kinds: A concept introduced by Saul Kripke to refer to basic names like those for water or the human species which retain their meaning in every context whatever, and which are “rigid designators” of their referents, not merely conventional signs but necessary in all worlds.

Source: What is Good? What is Bad? The Value of All Values across Time, Place and Theories’ by John McMurtry, Philosophy and World Problems, Volume I-III, UNESCO in partnership with Encyclopedia of Life Support Systems: Oxford, 2004-11.