Taxonomy

A taxonomy is a controlled vocabulary for classifying things. The classical form is a hierarchy — each item in exactly one place, categories nesting — which is precise and forces an impossible decision whenever something belongs in two places.

The alternatives address that directly. A faceted classification uses several independent dimensions at once: an item is described by its subject and its format and its audience, and any combination can be selected. A folksonomy abandons control entirely and lets people apply free tags, which captures vocabulary nobody anticipated at the cost of synonyms, misspellings, and singular-plural drift.

The choice of dimensions is the substantive design work. Classifying content by the purpose it serves rather than by the subject it is about is what allows the same material to be recombined for different audiences — a hierarchy organised around subject cannot do that, because the structural role was never modelled.

Two practical notes. A vocabulary is a shared model, so every near-synonym costs everyone a decision; preferring an existing term over a new one is the whole discipline. And separating a display label from a stable identifier means the label can be improved later without breaking anything that references it.