(m.); the observance in the Diaspora of the Major Holidays (Pesach, Shavuot and Sukkot) as two-day, rather than one-day Holidays, at both ends (except for Shavuot, which is observed simply for two days).
This two-day observance was instituted in Talmudic times because of the difficulty in communicating the decisions of the Sanhedrin in Yerushalayim as to the beginnings of the various Hebrew Months to the Jewish communities in the Exile, thereby creating confusion as to when certain holidays fell. Since the doubt was only over two days, the two-day observance covered both possibilities.
Despite the fact that for many centuries already, there has been no doubt about the time of the occurrence of the “Molad,” or the “New Moon,” Jews in the Diaspora continue to observe the two-day holidays because of the principle of “Minhag Avoteinu B’Yadeinu;” meaning that we retain certain of the customs instituted in ancient times so as to recall significant events in our People’s history.
The Sages had devised a method of torchlight communication by night from mountain-top to mountain-top to quickly alert the entire Diaspora of the decisions of the Sanhedrin with regard to the beginnings of the Month. But the Shomronim, the not-so-good Samaritans, frustrated their scheme by lighting torches on the wrong nights, thus forcing the adoption of the two-day system of Holiday observance in the Diaspora.