The premium at which an IPO's shares are reported to change hands unofficially before listing.
GMP is the amount above the issue price that dealers outside the exchange are reported to quote for an IPO's shares before they list. It is not published by NSE, BSE or SEBI, has no legal standing, and the trades behind it cannot be verified.
Different sources often report different figures on the same day. Xflot labels every GMP figure unofficial and keeps a record of how far the reported GMP was from the actual listing price.