Expression Sets, Decision Table, and Decision Matrix are three different key modules of Public Sector Solutions: Business Rules Engine (BRE). Expression Sets are modules that can define expressions that can be reused across multiple rules or matrices. Decision Table is a module that can evaluate data based on rows of conditions and actions in a tabular format. Decision Matrix is a module that can evaluate data based on columns of conditions and outcomes in a tabular format. Reference: https://help.salesforce.com/s/articleView?id=psc_admin_setup_bre.htm&type=5&language=en_US