The V-model is a type of software development lifecycle model where the development process executes in sequential phases shaped like a V. It emphasizes verification and validation activities that are planned and executed at each development stage. The key phases include requirement analysis, system design, module design, unit testing, integration testing, system testing, and user acceptance testing. The V-model has advantages like discipline, clarity for smaller projects, and early validation. However, it also has disadvantages like high risk, unsuitability for complex or changing projects, and lack of iteration or concurrency.