The placing of things into named classes. Classification imposes an order; it does not find one lying there.
From classify (Latin classis, a class, by way of French classifier, classis + facere, to make); the act of placing things under named divisions.
The order did not exist before someone drew it — sorting things into named classes is an act of authorship on the world rather than a report of a pattern already lying there, which is why two honest classifications of the same things can disagree without either being wrong.