Aaron Benton, an experienced architect, specializes in creative mobile application development with over 10 years of experience in full stack development. He currently works as an Applications Architect for Shop.com in Greensboro, North Carolina and is a Couchbase Community Champion. Definitions are used to create reusable sets of code within models, allowing for smaller and more efficient models. By defining definitions at the root of the model and referencing them using $ref, developers can reduce code duplication and make their models more maintainable. In this example, Aaron uses definitions to streamline his FakeIt model by creating a Phone definition that contains 3 properties: type, phone_number, and extension. He then uses this definition in two different places within his Users model to generate phones for the main phone number and additional phones. This approach allows developers to take advantage of definitions to create more efficient models while reducing code duplication.