To create a custom object in Object Definition form in SuccessFactors, follow these steps:

1. Log in to SuccessFactors as an Admin or an HR administrator with the necessary permissions.

2. Go to the Admin Center and select "Manage Data" under the "Employee Data" section.

3. Select "Object Definitions" and then click on "Create New" to create a new custom object.

4. Choose the base object type for your custom object, such as "Employee" or "Position."

5. Enter a name for your custom object and select the fields you want to include in the object. You can also define relationships with other objects, such as a one-to-many or many-to-many relationship.

6. Define the permissions for the custom object, such as who can view, edit, or delete data in the object.

7. Save the custom object definition and test it to ensure that it is working correctly.

8. Once the custom object is created, you can add data to it by going to the "Employee Data" section and selecting "Import Data" or "Add New." The custom object will appear as a separate tab in the Employee Data section.

It's important to note that the steps to create a custom object in Object Definition form may vary depending on the SuccessFactors module and version being used. Additionally, creating a custom object may require additional permissions or technical expertise.