The software development lifecycle (SDLC) is a process used to develop software in a systematic way. It includes stages such as requirements gathering, design, development, testing, deployment, and maintenance. Each phase has specific objectives, ensuring the final product meets user needs and quality standards. By following the SDLC, teams can improve productivity, manage project risks, and deliver software that is both effective and efficient. Various methodologies like Agile, Waterfall, and DevOps dictate how these stages are approached in different projects.