When the project management team and or the project management team leader is attempting to create and or establish a schedule that the project needs to follow over the course of its project life cycle, often times, in fact nearly always, the timing of the start of varying elements of the project is not entirely based on what the project management team or project management team leader feel is the ideal. Instead, typically here are constraints involved based on the resources that may or may not be available at a given time. This is referred to as resource leveling. More specifically speaking, resource leveling refers to a type of scheduling network analysis in which decisions as to start and finish dates are directly tied to constraints tied to those resources. For example, during certain times, there may be a deficit in resource availability, for one reason or another. During times like this it may be very difficult to begin a new phase of the project.
This term is defined in the 3rd and the 4th edition of the PMBOK.