The mapping target is an element in your code from which data can be obtained or that can accept data. Most typically, it is a property of your object, but it can also be a field, method, or an event.
The actual mapping target is represented by the ObjectMemberLinkingTarget class. When you use the attributes to define the live mappings, mapping target objects are created and maintained together with their Mappings, so normally you do not deal with them directly.