The SAP system landscape contains all installed R/3 Systems. It can consist of several system groups, whose R/3 Systems are connected with each other by transport routes.
Typical system groups are:
For further information on designing your system landscape, see the documentation on the Workbench Organizer:
R/3 library ® Basis Components ® ABAP Workbench ® Change and Transport Organizer ® Requirements for Working with the CTS.