Life Cycle (glossary)
(1) The organized collection of activities, relationships and contracts which apply to a system-of-interest during its life. (Pyster 2009, 73)
(2) The evolution of a system, product, service, project or other human-made entity from conception through retirement. (ISO/IEC/IEEE 2015)
(3) Development (life) cycles start with user needs and end with system decommissioning and disposal. Project cycles contain three aspects: business, budget, and technical. (Mooz, Forsberg, Cotterman 2003, 259)
Source
(1) Pyster, A.(ed.). 2009. Graduate Software Engineering 2009 (GSwE2009): Curriculum Guidelines for Graduate Degree Programs in Software Engineering. Integrated Software & Systems Engineering Curriculum Project. Hoboken, NJ, USA: Stevens Institute of Technology, September 30, 2009.
(2) ISO/IEC/IEEE. 2015. Systems and Software Engineering -- System Life Cycle Processes. Geneva, Switzerland: International Organisation for Standardisation / International Electrotechnical Commissions / Institute of Electrical and Electronics Engineers. ISO/IEC/IEEE 15288:2015.
(3) Mooz, H., K. Forsberg, H. Cotterman. 2003. Communicating Project Management. Hoboken, NJ, USA: John Wiley and Sons.
Discussion
For additional discussion of the different uses of "life cycle", see the Life Cycle Models article.