Non-performing assets (NPAs) are loans from banks that do not yield returns, defined by the Reserve Bank of India as loans overdue for more than 90 days. The document discusses the implications of NPAs on banks, including the need for provisioning and the ability for banks to recover debts through legal measures outlined in the SARFAESI Act. It also explains the classification of NPAs into gross and net NPA and the procedures for resale to asset reconstruction companies.