What is a System (too many definitions)....

The International Council on Systems Engineering (INCOSE) summarises the competing definitions of a System in their Glossary of Terms publication.

• An integrated composite of system elements that provide a capability that satisfies stated needs. (NAWCWPNS)
• A set of functional elements organized to satisfy user needs. (IEEE)
• An integrated composite of people, products, and processes that provide a capability to satisfy a stated need or objective. (MIL-STD-499B-UNAPPROVED))
• Any process that converts inputs to outputs.(Bahill)
• A composite of equipment and skills, and techniques capable of performing or supporting an operational role, or both. (MILSTD-721C, MIL -STD-280)
• A composite, at any level of complexity, of personnel, procedures, materials, tools, equipment, facilities, and software. (MILSTD-882B)
• A combination of two or more sets, generally physically separated when in operation, and such other assemblies and parts necessary to perform an operational function or functions. (DOD-STD-100C)
• The determination of the integrated quantitative and qualitative requirements for prime mission equipment, its supporting equipment and facilities, procedures (including computer programs), personnel selection and training, and logistics support. (CHASE)
• A combination of two or more interrelated equipment (sets) arranged in a functional package to perform an operational function or to satisfy a requirement. (DSMC)
• A set of functional elements organized to satisfy user needs. (IEEE P1220)
• The composite of equipment, material, computer software, personnel, facilities and information/procedural data that satisfies a user need. (SYSB-1)
• A composite of equipment skills and techniques capable of performing and/or supporting an operational role. (AFM), (MIL -E-6051 D)
• A set of interdependent internal systems (segments, elements, subsystems, components, and so on) which perform together as a defined functional unit. (NB Reilly Assoc.)
• An interacting collection of hardware, software, people, facilities, supplies, and procedures designed to accomplish a specified mission or
• objective. (Aero Ind)
• A collection of components organized to accomplish a specific function or set of functions. (IEEE 610.12-1990)
• A combination of inter-related items arranged to perform a specific function. (ARD50010-91)
• An organized arrangement in which each component arrangement in which each component part acts, reacts, or interacts in accordance with an overall design inherent in the arrangement. (AIR 1489-88)
• The complex or hardware and software utilized to affect the control of a process. (Aero Ind)
• In data processing, any group of software and hardware that is connect to operate as a unit. (SAE DICT)
• A composite of equipment, subsystems, skills,and techniques capable of performing or supporting an operational role. (MIL-STD-499A), (MIL-STD-463A)
• A combination of parts, assemblies and sets joined together to perform a specific operational function or functions. (DOD-STD-100C)
• A combination of inter-related items arranged to perform a specific function. (WATOG)
• A complex composite of devices and/or procedures to provide a desired functionality. (Aero Ind)
• A set or collection of interacting elements within a specified boundary. (Aero Ind)
• A device, procedure, or scheme which behaves according to some description, its function being to operate on information and/or energy and/or matter in a time reference to yield information and/or energy and/or matter.(Systems Philosophy, Ellis & Ludwig, Prentice-Hall, 1962)
• Orderly combination or arrangement as of particulars, parts, or elements into a whole; especially such combination according to some rational principle. (Black's Law Dictionary, 5th Ed., West Pub, St.Paul, MN, 1979)
• A combination of inter-related items arranged to perform a specific function. (Aero Ind)
• A regularly interacting or independent group of items forming a unified whole which performs one or more required functions. (Aero Ind)
• A composite of equipment, skills, and techniques capable of performing or supporting an operational role, or both. (Aero Ind)
• Includes all elements of equipment necessary for the control and performance of a particular major function. (FAA AC 120-42A)
• The concept of system is an abstract, devised synthetic entity. (adapted from W.P.Chase, Mgmt of SE)
• A combination of elements that will function together to produce the capabilities required to fulfill a mission need. (DFAR)
• An interacting combination of elements viewed in relation to function. (INCOSE Adopted and Recommended Definition)
• A term which describes the characteristic action, function, or conditions at the external boundaries of a combination of elements, components, or sub-systems which interact together. (draft NCOSE Terminology WG)
• A homogeneous entity that exhibits predefined behaviour in the real world and is composed of heterogeneous part that do not individually exhibit that behaviour.(DERA)
• An item or equipment designed to provide a required service to a set of users, and which is complex enough to consist of several interacting components. (WG6)
• A collection of components organised to accomplish a specific function or set of functions. (WG6)
• A system is defined to consist of a set of components which interact according to a design. (IEC 1508)