An identity document (also called a piece of identification or ID, or colloquially as papers) is any document which may be used to identify a person or verify aspects of a person's personal identity. If issued in a small, standard credit card size form, it is usually called an identity card (IC or ID card). Some countries issue formal identity documents, while others may require identity verification using informal documents. When the identity document incorporates a person's photograph, it may be called photo ID.