The organization information used in HR is as follows
1. Business Group
2. HR Organization
The HR organization classification used in oracle financials applications are as follows
1. GRE/Legal Entity
2. Operating unit
3. Company Cost Center(Used in financials DBI)
4. Auditable Unit(Used in ICM module)
5. Assets Organization (Used in Financial Payables : Assets)
With Oracle Human Resources, you can define multilevel organization hierarchies, with a business group at the top of each hierarchy. When you define new organizations, they are automatically assigned to the business group associated with your current session. Each organization is part of a business group. The business group is usually the top box on an enterprise organization chart, as shown in below figure.

 
The business group is the largest organization unit you set up in Human Resources to represent your enterprises as an employer. After defining one or more business groups for your enterprise, you set up one or more government reporting entities (GREs) within each business group. The GRE is the organization that federal, state, and local governments recognize as the employer.

Below this level, you represent the groupings in which employees work, such as branches, departments, or sections, by means of internal organizations. To enable the assignment of employees to an internal organization, you classify the internal organization as an HR organization.
You can define external organizations in the same way as internal organizations, so that you can represent organizations that are not part of your enterprise (such as training vendors or tax offices). The major difference between internal and external organizations is that you cannot assign people to an external organization.