Processes generally fall into one of three categories?

 Processes used once or at predefined points in the project. The processes DEVELOP Project Charter and Close Project or Phase are examples.  Processes that are performed periodically as needed. The process Acquire Resources is performed as resources are needed. The process Conduct Procurements is performed prior to needing the procured item.  Processes that are performed continuously throughout the project. The process Define ACTIVITIES may occur throughout the project life cycle, especially if the project uses rolling wave planning or an adaptive development approach. Many of the monitoring and control processes are ongoing from the start of the project, until it is closed out.