A vocabulary is the complete set of words and phrases that one or more people and/or organizations have at their disposal for reasoning and communicating about any topic. Since they are often interested in specific topics, terminologies may be subsets of their vocabularies.
In order for people (or organizations) to properly reason and/or communicate, they need a set of terms (and a semantics to provide their meanings).
- The set of words that you know is your vocabulary.
- The set of words listed in an English dictionary is a vocabulary of the English language (of its authoring organization)