Project Scope Statement:

Describes the project deliverables and the work required to create them. 
Provides also a common understanding of project scope among stakeholders.

May contain explicit exclusions from the scope that can help manage the expectations of 
stakeholders.

Enables staff to perform more detailed planning, directs the work of the same during execution and provides a baseline for evaluating whether requests for changes or additional work are contained in scope or are external to the project boundaries.

[Output of the process 5.3 Define Scope of the PMBOK® Guide Fifth Edition]