Lifecycle models are frameworks that describe the stages a product or project goes through from inception to retirement. These stages typically include development, introduction, growth, maturity, and decline. Each phase has distinct characteristics and challenges, helping teams understand how to manage resources and strategies effectively. In software development, lifecycle models like the Waterfall model and Agile methodology guide the process of creating and maintaining applications. These models emphasize different approaches to planning, executing, and delivering projects, allowing teams to choose the best fit for their specific needs and goals.