A custom field is a user definable property which may be stored against a particular data type. A custom field may be made available to the relevant data entry property sheet and to any relevant list windows.
For example, if you were to add a custom field, 'Job Number', to the task data type then you would be able to add job numbers to any task from within the task property sheet. Also, you would be able to view the job number of each task by displaying the 'Job Number' column in the task list in Diary mode.
Also, if you were to add a custom field, 'Birthday', to the contact data type then you would be able to record the birthdays for all contacts in OfficeTalk. You would be able to enter the birthdays from an additional property page in the Contact property sheet. You would be able to view the birthdays of a contact by adding the 'Birthday' column to the contact list in Directory view. Additionally, you would be able to add the 'Birthday' field to the Contact view.
Custom fields are also available from the search dialog boxes making it possible to include any custom field when performing both simple and advanced searching. Equally, custom fields are available from the print dialog boxes so that any data held in custom fields may be printed in just the same way as the system fields.