• To make Active Directory more manageable, it is divided into these partitions:
• Domain partition that holds the user accounts, computers accounts, and other domain-specific information
• Configuration partition that holds general information about the Active Directory forest
• Schema partition that holds the definitions of all objects and object attributes for the forest
• Application partitions can also be created by an administrator to hold application-specific information. A global catalog server is a domain controller that holds a subset of the information in all domain partitions.

Read more about Active Directory Application Partitions at:
http://articles.techrepublic.com.com/5100-6345_11-5746279.html.