Software maintenance is a fundamental and ongoing phase within the software development lifecycle focused on modifying a software product after delivery to correct faults, improve performance or other attributes, or adapt the product to a modified environment. As an academic concept and research field, it investigates the processes, methodologies, tools, and challenges associated with these post-deployment activities. This encompasses understanding existing complex codebases, managing the evolution of systems, mitigating technical debt, and developing efficient and effective strategies for corrective, adaptive, perfective, and preventive changes, highlighting its critical significance in ensuring software longevity, reliability, and continued value.