Geshem (גשם) is one of the Hebrew words for "rain," applied mostly to the heavy rains which occur in Israel in the fall and winter. This half of the year is called in the Mishnah "yemot ha-geshamin" (days of rains). In the liturgy of the German-Polish ritual "Geshem" stands for the piyyuṭim which in the Mussaf or additional service for the Eighth Festival Day (Shemini Aẓeret) are read and sung as an introduction to the first mention of the "powers of rain," i.e., the words "He causeth the wind to blow and the rain to descend."
"Geshem" corresponds to the "Tal" (Dew) occurring in the liturgy for the first day of the Passover, when the above-quoted passage is omitted as being inapplicable to spring and summer. These piyyuṭim end with an invocation in six stanzas, each of which closes either with "for his sake do not withhold water!" or with "through his merit favor the outflow of water!" the merits of the Patriarchs, of Moses, of Aaron, and of the twelve tribes crossing the Red Sea being successively referred to.