The document discusses Model-View-ViewModel (MVVM), a software architectural pattern. It separates an application into three main logical components: the model, the view, and the view model. The model represents the data and business logic. The view displays the UI and handles user input. The view model acts as an intermediary between the model and view, preparing the model data for display and passing user input to the model. The document provides examples of each component and notes how data binding and events allow the view and view model to communicate without directly referencing each other. It argues that MVVM promotes loose coupling, testability and maintainability.