This link will be useful for your guidance on ECB: http://rbidocs.rbi.org.in/rdocs/notification/PDFs/09MCEC300611.pdf
It is a kind of loan to be raised from outside india in various form buyers credit, suppliers credit, loan from International financial institution etc for the tenure of not less than 3 years.
RBI has put cap on borrowing limits as well its end use vis a vis interest rate. It is generally 500 basis points + LIBOR.
Many listed companies have raised ECB due to advantage of cheapter interest rate as well no risk of dilution in equity of the company.