Area Binding 
The context that you specify for this property defines the visibility and lifetime of the area instance versions of the instance. Possible contexts are:
Application server
Area instance versions exist until the application server is shut down.
User session
Area instances exist until the last external session of the current user session ends. A user session is the status between the logon and logoff of a user on an AS ABAP. For area binding, every user logon to an AS ABAP counts individually. This also applies in particular when users log on via external interfaces such as RFC or ICF.
Top level transaction
The top level transaction is the first program in a call sequence. Such area instances exist for as long as the ABAP memory assigned to a call sequence, that is, for as long as the internal session of the top level transaction is loaded.