Section 2(12) of the Companies Act defines the term "debenture" which includes debenture stock, bonds and any other securities of a company, whether constituting a charge on the assets of the company or not. In a simple meaning, a debenture means a document, which either creates a debt or acknowledges it, any document which fulfills either of these conditions is a debenture. It may be defined as a certificate of debt or loan given under the common seal of the company evidencing that the company undertakes to pay specified amount with interest. Debentures are not part of share capital, it is a loan capital and company is liable to pay interest thereon whether there are profits or not. Debentures may be secured by way of creating charge on the assets of the company or by way of mortgage of company's property.
You will file Form-23 and Form-8 if it is secured and Form-10 if it is series of debentures with ROC.