The "Waterfall" model is a linear project management approach used primarily in software development. It consists of distinct phases, including 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 teams stay organized. However, it can be inflexible, as changes in requirements after a phase is completed can be challenging to accommodate. Despite its limitations, the Waterfall model is still popular for projects with well-defined requirements and low uncertainty.