The glossary activity module allows participants to create and maintain a list of definitions, like a dictionary. Glossary can be used in many ways. The entries can be searched or browsed in different formats. A glossary can be a collaborative activity or be restricted to entries made by the teacher. Entries can be put in categories. The auto-linking feature will highlight any word in the course which is located in the glossary.
Read more about the glossary module in the official Moodle documentation.