To be used when discussing the philosophical concept of universals.
According to Boethius (ca. 480-524)
A universal has to be common to several particulars
in its entirety, and not only in part
simultaneously, and not in a temporal succession, and
it should constitute the substance of its particulars.
To say of some particular thing that it has some kind of generic property (or higher-order relation), type (or higher-order kind) that all things of that nature exhibit or manifest. By way of example, to start by giving an ostensive definition, the greenness shared by all green things and the humanity shared by all individual persons count as universals.
An explanation of what is meant by the parenthetical "higher-order" in the preceding paragraph. Take location to be a universal property of all things with extension. Then the universal relation of next to hinges on the notion of location. Take humanity to be the universal/essential category belonging to all individual persons. Then the universal kind of mammal encompasses the notion of humanity.
Discussions of universals can be traced right back to the dawn of Western Philosophy, back to some of Plato's dialogues (Parmenides, Phaedo, Republic (esp. books V-VII;X), Sophist) and Aristotle's monographs (Categories, Metaphysics) -- all to be found at the Internet Classics Archive hosted by MIT.