Data partitioning is a database technique commonly used to improve performance and manageability.  Salesforce provides a feature called Divisions that lets you partition your records into logical sections. As an example, you can divide your customer records based on their geographical location by creating divisions called US, EMEA and APAC.  The users in these regions can then be enabled to use these division. One of the benefits of doing so would be that division specific searches and division specific list views will provide them with data that is most relevant to them.  The other potential benefit is performance.  I was recently working with a customer with very large data volumes and partitioning the records into divisions significantly improved reporting performance.

Divisions have to be explicitly enabled for your organization by Salesforce. Divisions can be used with both standard and custom objects.  Effective usage of divisions require that you understand the usage pattern, criteria used to create the division, optimal number of divisions to create, data distribution between the divisions and data growth pattern. To get started look at online help or this cheat sheet.