Backbone.Model: Models are the entity of an application that store data and contain some logic around data such as validation, conversion, and data interaction.

Backbone.View: Views present an idea of organizing your Document Object Model (DOM) interface into logical blocks, and represent the model and collection data in them. Views are excellent tools to organize all the JavaScript event handlers and to add dynamic HTML content in your application via optional use of JavaScript templates. As Backbone follows an MV* pattern, Backbone views mostly work as presenters and take care of the major portion of application functionality.

Backbone.Collection: A collection is a group of models. A collection includes a lot of functionality as well as Underscore utility methods to help you work on multiple data models.

Backbone.Router: A router provides methods for routing client-side pages and acts subsequently whenever there is a change in the browser's URL. A router maintains the application state as per the URL change.

Backbone.Events: Events are an important concept in Backbone, since they provide a mechanism to use the PubSub pattern and decouple your application components.