A Mapping Parameter is a static value that you define before running the session and its value remains until the end of the session. When we run the session PowerCenter evaluates the value from the parameter and retains the same value throughout the session. When the session run again it reads from the file for its value. A Mapping Variable is dynamic or changes anytime during the session. PowerCenter reads the initial value of the variable before the start of the session and changes its value by using variable functions and before ending the session its saves the current value (last value held by the variable). Next time when the session runs the variable value is the last saved value in the previous session.