This document provides an introduction to MDX (Multidimensional Expressions), which is the query language used for multidimensional databases. It explains that MDX allows for very concise queries with relatively complex results, such as year-to-date, rolling averages, and net performance. The document also discusses key MDX concepts like cubes, measures, tuples, and sets. It provides an example MDX query and demonstrates how to use functions like WITH, MEMBER, TOPCOUNT, and WHERE to retrieve specific data from an Analysis Services cube.