The V-model is a software development model where testing occurs in parallel with each phase of development. It involves first creating test plans based on requirements, then performing integration, component, and unit testing as the system is designed and coded from high to low level. The V-model is simple to use, allows defects to be found early, and works well for small projects with clear requirements. However, it is rigid and does not allow for early prototypes. It is best suited to small-medium projects where requirements are fixed and technical expertise is available.