The Waterfall model is a linear project management approach used primarily in software development. It consists of distinct phases: requirements gathering, design, implementation, testing, and maintenance. Each phase must be completed before moving on to the next, making it easy to understand and manage. This model emphasizes thorough documentation and planning, which helps ensure that all requirements are met before the project progresses. However, its rigidity can be a drawback, as it does not easily accommodate changes once a phase is completed, making it less suitable for projects with evolving requirements.