The PMBOK guide defines the 5 project management process groups as follows
Initiating Process Group: Defines and authorizes the project
Planning Process Group: Plans the course of action required to attain project objectives and define the scope of the Project.
Executing Process Group: Integrates people and other resources to carry out the project plan for the project.
Monitoring and Controlling Process Group: Regularly measures and monitors the activities of the project so that corrective action can be taken when needed.
Closing Process Group: Formalize the acceptance of the Project and brings the Project to an orderly end