What is vocabulary ? What is vocabulary ? Broadly defined, vocabulary is knowledge of words and word meanings. Vocabulary is "all the words know and used by a particular person". vocabulary is the foundation of language, our most effective communication tool. Advance Advance Vocabulary Building…… Vocabulary Building…… Vocabulary building means increasing the vocabulary. Vocabulary development refers to the knowledge of stored information about the meanings and pronunciations of words necessary for communication. Knowledge of word parts can play a role in increasing our vocabularies. Word parts include prefixes, suffixes, and root words.