The body of words used in a particular language
(B. Russell's term for) the residual vocabulary of a body of knowledge after analysis, i.e. the set of words (or symbolic expressions) that are sufficient to express every proposition in that field (e.g. mathematics, logic, history, geography, or human experience in general) and such that no word in the vocabulary can be defined in terms of the other words in it; the ultimate object-vocabulary of any field of knowledge or beliefs.
A vocabulary of words that a person understands passively but may not be able to generate (opposed to active vocabulary).