Scope

The boundaries of the project by defining what the project should focus on (includes) and shouldn't focus on (excludes). The purpose is to remind and unify the team around what specific problem they're trying to fix, to keep the project at a manageable level (not too big or too small), and to prevent the project from driving in the wrong direction (i.e., avoiding "scope creep").
Related StatStuff Video: 
   -Section 4-Define Phase, Lesson #3 - Defining a Project Scope