Communications between human are largely based upon language. Learn a new language involves many processes. One step is to learn and build a vocabulary. Vocabulary is comprised of the different words used by speakers to express themselves. Linguists recognize two different types of vocabulary: passive and active.
The term passive vocabulary refers to the words that one has learned or is familiar with. Words that comprise a person's passive vocabulary are used frequently for several reasons. First, their definitions are not always completely known. In other cases, speakers avoid certain words or terms that they do not need to use often in conversation. For most people, their passive vocabulary is much larger than their active vocabulary. This is because passive vocabulary continues to expand throughout a person's lifetime.
Active vocabulary is the set of words that a person can produce, such as when speaking or writing. Many linguists agree that a person's active vocabulary is usually smaller than his or her passive vocabulary. This is because words are only added to the active vocabulary as they are needed. In other words, a person will not add a word to active vocabulary unless he or she needs it to communicate.
This is a record from Robin, an English native speaker from British. Appreciating his generous help.