Format type & is already in use

What causes this issue?

This format type cannot be deleted because it is used in other tables.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

To delete the format type, proceed as follows:
-- Press F3 to return to the list of format types.
-- From the list, call the delete function again. You will see a list
of tables, in which this format type is used.
-- You must delete the format type from these tables before it can
be deleted from the list of format types.

Error message extract from SAP system. Copyright SAP SE.