Decision support systems (DSS) are computer-based tools that assist organizations in decision-making by compiling information from various data sources to solve problems and enhance decision quality. They can be categorized based on user interaction (passive, active, and cooperative) or mode of assistance (communication-driven, data-driven, document-driven, knowledge-driven, and model-driven). Additionally, expert systems, a subset of DSS, simulate expert decision-making in specific domains, but face challenges like user accessibility, knowledge updates, and the complexities of rule management.