Jacoby 2NT is used after partner opens a major and you have at least 4 card support and 12+ pts.
It is used to separate weak distributional raises to game, from hands with slam interest -
Jump to game with a 7 loser, few points and no slam interest (fast arrival). e.g. 1H - 4H
Use Jacoby 2NT with a fit, opening points and slam potential. e.g. 1H - 2NT
Oswald (Ozzie) Jacoby (1902 - 1984) - Ozzie Jacoby was one of the world's best players and writers for fifty years. In the '30s, Jacoby played on the famous Four Aces Team that won several national events. Ultimately he would win 30 national championships, his last at the age of 81.
As a bridge columnist, he penned 10,000 articles. Jacoby was also an ardent patriot, serving in the armed forces in WWI (at 15), WW2 and the Korean War.