Explanation/Reference:
http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.6/getting_started/configuration/guide/ gs36cnov.html#wpmkr1279022 Building the Target Configuration The target configuration is effectively the cumulative result of the current running configuration with the user-entered configuration. In other words, it is the user-intended configuration if the user were to commit the entered configuration changes. Each user has its own unique target configuration that is not visible to others. However, the latest router running configuration is visible to every user and it forms a base to each user's target configuration instance.
A user can populate the target configuration changes from a previously saved file and browse or modify configuration changes in the target without affecting the current running (that is, active) configuration on the router. The router running configuration can never be set directly. All changes to the running configuration must go through the target configuration where it is explicitly committed by the user to become part of the router's running configuration.
A unique target configuration is created implicitly when the user enters the configuration mode. The target configuration is not a copy of the running configuration; instead, it is an overlay of configuration changes, entered by the user, which have not been committed yet, on top of the router's running configuration. When the user enters the first stage of the configuration and prior to entering configuration changes, the target configuration is identical to the running configuration. This is also the case after each successful commit operation, where the target configuration and running configuration are identical. The user can browse the configuration changes made in the current session but not yet promoted to the active configuration, by using show configuration. The user can also browse the resultant configuration produced via the merger of uncommitted configuration and the router's active (also known as running) configuration by using show config merge.
This is essentially the session's target configuration.