Project management is essentially aimed at producing an end-product that will effect some change for the benefit of the organisation that instigated the project. It is the initiation, planning and control of a range of tasks required to deliver this end product, which could be a physical product, it could be new software or something less tangible like a new way of working.
A key factor that distinguishes project management from just management is that it has this final deliverable and a finite timespan, unlike management which is an ongoing process. Because of this a project manager needs a wide range of skills; often technical skills, certainly people management skills and good business awareness.
For all but the simplest projects a formal approach to managing a project works best. The control imposed by a formal approach is essential when there are complexities such as new technology, inter-dependent tasks, teams spread across several departments or companies, or where teams are located in different parts of the world; all common occurrences in many business projects.
Because every project will involve some type of change, change management is an integral part of the PM process. And because there is change there are likely to be risks so risk management is also thrown into the project management mix.
There are standard project management processes used to plan and control tasks, budgets and schedules, to communicate between the different people involved and deal with risks. These processes are usually ongoing throughout the project.
There are also various phases of a project that will have a defined start and end within the overall project lifespan. For instance, the requirements gathering phase often occurs in the early part of the project.