Web Dynpro Component 
A Web Dynpro component is a reusable entity. It summarizes all components that are required as part of this programming unit for an executable Web Dynpro application.
The Web Dynpro component concept offers a number of advantages:
Structuring the programming
Creation of easily manageable application blocks
Reusability of whole components
Decoupling of software projects in both time and space
The Web Dynpro component contains any number of windows and views and their corresponding controllers. Additional Web Dynpro components can also be referenced.
The creation of a Web Dynpro component is always mandatory, since the existence of the Web Dynpro window and the views and controllers that it contains is linked to the existence of the component itself. Communication between the elements of two Web Dynpro components and their call by a user is implemented using the component interfaces, so it does not make sense to consider the individual parts of the component separately.
A Web Dynpro component can embed other Web Dynpro components, and correspondingly a Web Dynpro component can be embedded in any other Web Dynpro components. This communication also takes place over the component interfaces.
Lifetime of a Web Dynpro Component
A Web Dynpro component’s lifetime begins the first time it is called at runtime, and ends with the lifetime of the Web Dynpro application that called and thereby instantiated the component. For embedded components this means that during the lifetime of the embedded component, they are not instantiated until the moment when they are required. Their lifetime ends, however, at the same time as the embedded component when the Web Dynpro application that was originally called is ended.
It is also possible for the embedding component to create or destroy the embedded component using an appropriate API and thus control its lifetime.