MDX (Multidimensional Expressions) is a query language for OLAP (Online Analytical Processing) databases, primarily used with Microsoft SQL Server Analysis Services (SSAS) and other multidimensional database systems. Unlike SQL's flat relational model, MDX navigates hierarchical cube structures with dimensions, measures, and complex aggregations. Its syntax resembles spreadsheet formulas and enables sophisticated time-based calculations, drill-down operations, and dynamic filtering across multiple dimensions—making it essential for business intelligence reporting and data analytics where users need to slice, dice, and pivot multidimensional data rapidly.