RONF is a standard style of responding to an opening weak two that employs the following bids:

2NT	Strong (15+ points), artificial, and forcing for one round. Opener is expected to bid his cheapest side suit with an ace or king in it, if he has any (otherwise he rebids his suit).
Single raise	Natural signoff. The response from which RONF gets its name.
New suit	Natural (5+ cards) and forcing for one round.