OLAP is short for Online Analytical Processing. It is a category of tools that allow data analysts to analyze multidimensional data.
An OLAP server is a tool that sits between the data warehouse and your computer. The OLAP server understands how data is organized in the database and has special functions for aggregating and presenting that data.
Common OLAP servers include products such as Essbase from Hyperion and SQL Server with Analysis Tools from Microsoft.
An OLAP server will take a few hundred million records from a data warehouse and create a multi-dimensional data structure. This structure, known as an OLAP cube, will make querying faster.