Models are objects in Ember that represent data that can be displayed to users. They are persistent and won't be lost when the user closes the browser window.

Many models are loaded from data that is stored in a server from a database. Typically, the data is sent back and forth as a JSON representation. This is where Ember Data comes in. Ember Data is included by default when you create an application in Ember. It helps retrieve data, store data locally, and save information to the server.

Ember Data can be configured to work with many different types of databases and servers. If used properly, Ember Data can help manage your application models without the use of multiple Ajax requests throughout your application.