A set of project phases generally executed sequentially. Output of each of the previous phases are used as inputs to the subsequent phases. This is a logical way of breaking the project into manageable pieces.

It is important to understand that Project Life Cycle and Process Phase groups are very different. In fact in each phase of the life cycle one or more of the process groups' processes are performed

The application area dictates the type of project life cycle that should be used.

For example SDLC or Software Development Life Cycle is used for Software Development , Construction Industry would have their best practice life cycle etc.

Product life cycle is different from project life cycle