Everyone has both a receptive vocabulary and a productive vocabulary. Combined, they hold all the words we know.
A vocabulary is well known to be all the words a person knows. A receptive vocabulary describes all the words a person understands, and is also called a comprehension vocabulary. A productive vocabulary describes all the words a person can say or sign, and is also called an expressive vocabulary.
For babies and adults learning a language, it’s not uncommon for them to be able to understand more words than they can say. This is especially true for babies learning language. In this case, their receptive vocabularies are bigger than their productive vocabularies. As an infant learns how to say or sign words, their productive vocabulary grows.
Aahnix is a Project Coordinator in the Bergelson lab at Duke University