Amidah (Hebr. standing prayer) – an alternative name for Shmoneh Esreh (Hebr. eighteen), a prayer which originally contained eighteen blessings; the nineteenth blessing was added in the 2nd century CE. Amidah, the main prayer of daily liturgy, is recited during the morning (shacharit), afternoon (mincha) and evening (maariv) service. On Shabbat, holidays and new moon, a shorter version, called mussaf, is used. Amidah is recited in a low voice, in a standing position, with both feet brought together, and the praying person must face Jerusalem. Amidah must not be interrupted before it ends.
From: J. Tomaszewski, A. Żbikowski, Żydzi w Polsce. Dzieje i kultura. Leksykon, (2001).