What is Software Life Cycle?

A software life cycle model (SLCM) is a representation of the major components of software development work and their interrelationships in a graphical framework that can be easily understood and communicated.
The Software Life Cycle begins when an application is first conceived and ends when it is no longer in use. It includes aspects such as initial concept, requirements analysis, functional design, internal design, documentation planning, test planning, coding, document preparation, integration, testing, maintenance, updates, retesting, phase-out, and other aspects.
You must have a defined SLCM for your project to:

• Determine project milestones at which project performance can be evaluated
• Define the sequence of work units
• Provide a framework for definition and storage of the deliverables produced by the project
• Communicate your development strategy to project stakeholders
  

A SLCM achieves this by:

• Providing a simple graphical representation of the work to be performed
• Allowing focus on important features of the work, downplaying excessive detail
• Providing a standard work unit hierarchy for progressive decomposition of the work into manageable chunks
• Providing for changes (tailoring) at low cost