Software-defined networking is an architectural paradigm and research domain that decouples the network control plane from the data forwarding plane, enabling network infrastructure to be programmatically managed and configured via software applications. As a field of study, it investigates novel network architectures, centralized control mechanisms, and the abstraction of underlying hardware to achieve greater network flexibility, agility, and innovation. Key characteristics include centralized or logically centralized control, network programmability through open interfaces, and dynamic resource management, holding significance for research into advanced network services, security, and optimization.