The textbook explicitly states under the classification of debentures from the point of view of tenure that 'Irredeemable debentures are also known as Perpetual Debentures.' The key characteristic is that the company does not provide any undertaking for repayment during its lifetime. These debentures are only repayable upon the winding-up of the company or after a very long period. This makes the given statement factually correct as per the NCERT textbook content.