Window: Inbound and Outbound Plugs 
Just like each view, each window has a number of inbound and outbound plugs.
Inbound Plugs
On the Inbound Plugs tab page you can create a number of inbound plugs for the window that is currently being edited. Enter a new name for this plug and add a description of it.
The properties of a window's inbound plug differ from a Inbound Plugs of View by the characteristics Interface and Startup or Resume that can be maintained.
Interface
This checkbox determines whether the window’s inbound plug only is used for navigation within the component, or whether the inbound plug should also be visible externally as part of the Component Interface. If the Interface checkbox is selected, the inbound plug that is now externally visible is also displayed as part of the interface view belonging to the window in the object list node Component Interface. However, you can change an inbound plug in the WIndow Editor.
Startup and Resume
Caution
The properties Startup and Resume are only relevant to inbound plugs of the interface view.
The Start Up property means that a Web Dynpro application can be started using this plug. When you create a Web Dynpro Application, you can only select these interface view inbound plugs that are selected as a startup plug.
Such inbound plugs that do not not have the property Start Up are available exclusively for navigation to an already-running application.
More information: Web Dynpro Window and Suspend/Resume Calls.
Event Handler and Parameters of Inbound Plugs
Unlike outbound plugs, inbound plugs can be equipped with an event handler. This event handler of an inbound plug is always called if the window is controlled using precisely this plug. The WDEVENT object of this handler method has the parameter IF_WD_APPLICATION=>ALL_URL_PARAMETERS of type IHTTPNVP. All application-specific URL parameters are stored in this table.
More information: Window: Inbound and Outbound Plug Parameters
Note
If an inbound plug has importing parameters, values must be available at runtime for these parameters. You can either provide these values by maintaining default values at design time or by transferring them as URL parameters with the call URL of the application.
More information: Using Parameters to Call a Web Dynpro Applications
Outbound Plugs
Parallel to inbound plugs, a window can have outbound plugs. You can use an outbound plug to leave a window for a view of an embedding window. Outbound plugs can be called in two different ways:
Using generated method WD_THISFIRE_<MY_OUTBOUND>_PLG
Using the generic method FIRE_PLUGof API IF_WD_VIEW_CONTROLLER for the current controller.
Even the outbound plugs of a window have two additional checkboxes compared with a view’s plugs: Interface and Exit or Suspend.
Interface
This checkbox determines whether the window’s outbound plug alone is used for navigation within the component, or whether the outbound plug should also be visible externally as part of the component interface.
If the Interface checkbox is selected, the outbound plug that is now externally visible is also displayed as part of the interface view belonging to the window in the object list node Component Interface. However, you can change an outbound plug in the WIndow Editor.
Exit and Suspend
Caution
The properties Exit and Suspend are only relevant to outbound plugs of the interface view.
If an embedded window is exited via a plug flagged with the property Exit, the component associated with this window is automatically closed. Calling an exit plug in the outermost component of a component usage chain leads to the whole Web Dynpro application ending.
More information: Web Dynpro Window
Outbound Plug Parameters
You can specify importing parameters for all outbound plugs of an interface view. These parameters are passed to the outbound plug when method WD_THISFIRE_<MY_OUTBOUND>_PLG is called.
More information: WD_THIS and the Local Controller Interface
The special parameter URL can be defined for an exit plug. If it is, once the plug has been triggered and the Web Dynpro application closed, the page specified in the parameter is opened. If the parameter is not defined, a standard exit page is opened. You can also define an exit page in transaction SICF.
More information: Application Logoff Page
More Information
You can find basic information about the plugs of a window in Window Plugs.