In the database world, partitioning is the horizontal splitting of rows in a table or index defined on a table in separate, smaller logical units. In fact, every table in SQL Server 2005 has at least one partition. You are essentially breaking one table or index up into smaller tables or indexes that act as one table or index. This can greatly increase performance because you are querying several smaller tables rather than one much larger one. The advantages increase when the server has multiple processors, which allow the partitions to be queried in parallel in the same query, and when the partitions are spread across multiple file groups.
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Creating Table Partitions in SQL Server 2005 
