When the project management team and or the project management team leader is trying to take a good overall look at the entirety of a project, it is helpful to put the project in some sort of a graphical mechanism in which it can easily be determined when each phase or activity of the project is to take place and how long its duration should be. In the process of doing that, it is imperative that a reliable and consistent means of determining exactly when each particular activity is scheduled to begin, how long it is estimated or expected to take to continue, and when the particular activity is expected to conclude. As part of this organizational technique, this is where the concept of the predecessor activity comes to play. A predecessor activity refers specifically to the work schedule activity that is part of the project that determines or establishes when the activity that is determined by the project management team and or project management team leader to be the logical successor activity can begin or end.
This term is defined in the 3rd and the 4th edition of the PMBOK.