(1) The behavior that system is expected to exhibit. (ISO/IEC/IEEE 24765 2010)
(2) Work to be performed under a contract or subcontract in the completion of a project. Also called work scope. (BusinessDictionary.com)
(3) The goals, processes, resources, facilities, activities, outputs and outcomes an organization is responsible for. (Created for SEBoK)
(1) ISO/IEC/IEEE. 2010. Systems and Software Engineering - System and Software Engineering Vocabulary (SEVocab). Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC)/ Institute of Electrical and Electronics Engineers (IEEE). ISO/IEC/IEEE 24765:2010.
(2) BusinessDictionary.com, s.v. "Scope." Available online at: http://www.businessdictionary.com/definition/scope.html. Accessed July 7, 2012.
(3) This definition was developed for the SEBoK.
Definition (1) is a typical systems engineering definition, outlining the range of behaviors/functions expected within a system. Definition (2) refers to the concept of "scope of work", as defined between an acquirer and a supplier. Definition (3) is important to the scope of an organization versus the scope of a system.