Migration is a synonym for heterogeneous system copy.
Your SAP system is converted from non-Unicode to Unicode. This can also be done as part of a homogeneous or heterogeneous system copy.
A system that resides on more than one physical or virtual hosts in a network, and can be accessed transparently as an entity.
SOURCE SYSTEM AND TARGET SYSTEM
The SAP system containing the original database is called the source system and the system to which the database copy is to be imported is called the target system.