This document provides an overview of the MDX (Multidimensional Expressions) language used with SQL Server Analysis Services (SSAS). It discusses key MDX concepts like tuples, cells, and sets which are used to access and retrieve data from multidimensional cube structures. The document explains how MDX differs from SQL and covers important MDX clauses like SELECT, WITH, and NON EMPTY. It also demonstrates how to use sets, functions like CrossJoin and Members, and calculated members in MDX queries.