A vocabulary is a set of defined terms — classes, properties, named individuals — that a community maintains together: the kinds of chemical entity a project works with, the concepts of a domain, the categories of a classification. On the network a vocabulary is a maintained resource of a space, typed as an ontology, with a namespace of its own under which its terms are minted.

Each term is its own nanopublication, signed by whoever defined it, so a vocabulary is not one document but a growing collection of small, individually attributable definitions. It is the most common kind of maintained resource on the network.