Define Waterfall model of System Life Cycle.

The Waterfall model is a traditional and linear approach to software development within the System Life Cycle (SLC). It follows a sequential and phased structure, where progress is seen as flowing steadily downward through several defined phases. Each phase in the Waterfall model must be completed before moving on to the next, and it is challenging to revisit or revise a phase once it's finished. The key phases of the Waterfall model include:

1. Requirements Gathering and Analysis:
   The project begins with a comprehensive analysis of customer requirements. Stakeholders collaborate to define the project scope, objectives, and specific functional and non-functional requirements.

2. System Design:
   Based on the gathered requirements, the system design phase involves creating a detailed blueprint for the system. This includes architectural, database, and user interface designs, outlining how the software will meet the specified requirements.

3. Implementation:
   In this phase, the actual code for the software is developed based on the system design. Programmers write, compile, and integrate the code, creating the functional components outlined in the design phase.

4. Testing:
   The completed software undergoes rigorous testing to ensure that it functions according to the specified requirements. This phase includes unit testing, integration testing, system testing, and user acceptance testing.

5. Deployment:
   Once testing is successful, the software is deployed to the production environment or released to end-users. This phase involves installing the software, configuring any necessary settings, and making it available for use.

6. Maintenance and Support:
   After deployment, the system enters the maintenance phase, where updates, bug fixes, and improvements are made as necessary. This phase can extend throughout the system's operational life.

The Waterfall model is straightforward and easy to understand, making it suitable for projects with well-defined and stable requirements. However, it has limitations in accommodating changes after the development process has started, as revisiting earlier phases can be time-consuming and costly. Despite its rigidity, the Waterfall model has been widely used in various industries, particularly for projects with clear and unchanging objectives.