As a noun, scope
is defined as "the area covered by a given activity or subject," and as a verb it's "to examine or investigate." In project management, it is both. The scope of the project refers to "the area to be covered" by this project. That scope calls out what's included and what the boundaries are—what's in, what's out. As an action, "scoping the project" refers to examining and investigating to determine which areas must be covered (e.g., what deliverables should be produced) in order to ultimately meet the project's business objectives.
In project management, the scope of a project is the sum total of all of its output products or results or deliverables—whatever the project is supposed to accomplish, expressed in terms of requirements. A scope statement of some kind is developed to ensure that
the project plan will include all the work required, and only the work required, to complete the project successfully. That statement is concerned with clearly defining and controlling what is and is not included in the project.
Why is the "is not included" portion important? It's important to know where the boundaries are to keep the project effort focused. It's all too easy for new features, items, components to get added to a project. They may be nice to have, but they may not be more important that other features or components, and specific deadlines by which those more important components should be delivered.
The beginnings of the project's scope definition is usually included in a Project Charter or similar document that is written during project initiation. The charter communicates what a project is being commissioned to do, and includes a high-level statement of project objectives and any assumptions about the scope required to meet those objectives. As the team starts detailed investigation and planning for the project, the scope is defined by updating the charter, or creating a separate scope document in some form. (See our Project Vision document and Project Statement of Work for two examples.) Whatever the exact form of document, the goal is to capture the project objectives, the deliverables to produce, and the work effort to create those deliverables. Ultimately, the scope will end up being expressed by all the work that shows up in the Work Breakdown Structure for the project—the foundation of the project plan and schedule. For more on how the WBS expresses the project scope in work form, see our guideline Planning and Scheduling: Task Identification and Work Breakdown.