A rules engine is a type of software that uses a set of pre-defined rules to make decisions, analyze data, or provide outputs based on input data. These rules can be defined by the user, and can be based on a wide range of criteria, such as business logic, regulations, or industry standards. Rules engines are commonly used by business and other organizations to automate decision-making processes, reduce the need for manual analysis, and improve the consistency and accuracy of decisions. They can be integrated with other software systems, such as databases and workflow tools, to provide a flexible and customizable way of processing and analyzing data.