NBFIs are non-banking financial institutions that are registered under the Companies Act and regulated by the RBI. They provide banking services like loans and deposits but do not accept demand deposits. NBFIs have more flexible regulations for foreign investment compared to banks. Banks are regulated under the Banking Regulation Act and are authorized to accept demand deposits and are part of the payment and settlement system. Some examples of large NBFIs in India are HDFC, Power Finance Corporation, Reliance Capital, and Muthoot Finance.