To delete an entity, you must first be in the edit mode so that you review the entity in its entirety before deletion. You'll not be able to delete a referenced entity. Example: Assume you have referenced 'Rubber' industry in one of your lead or contact. You'll not be able to delete 'Rubber' industry since it is referenced.
Review the contents and click on delete.
Referenced entities cannot be deleted. If Industry 'Rubber' is referenced (like it is shown in the picture above), you'll not be able to delete 'Rubber'. To delete a Contract, first delete all the visits made against it.