An OLAP cube is a method of storing data in a multidimensional form, generally for reporting purposes. In OLAP cubes, data (measures) are categorized by dimensions. OLAP cubes are often pre-summarized across dimensions to drastically improve query time over relational databases. The query language used to interact and perform tasks with OLAP cubes is multidimensional expressions (MDX). The MDX language was originally developed by Microsoft in the late 1990s, and has been adopted by many other vendors of multidimensional databases.
Although it stores data like a traditional database does, an OLAP cube is structured very differently. Databases, historically, are designed according to the requirements of the IT systems that use them. OLAP cubes, however, are used by business users for advanced analytics. Thus, OLAP cubes are designed using business logic and understanding. They are optimized for analytical purposes, so that they can report on millions of records at a time. Business users can query OLAP cubes using plain English.