Kedushah (Holiness) is the name of several prayers recited during Jewish prayer services. They have in common the recitation of two Biblical verses - and . These verses come from prophetic visions in which angels sing the verses, "Holy, Holy, Holy" as praises to God.
There exist several variations of the Kedushah, which appear in different contexts and have different laws. The best-known Kedushah is recited in the Amidah. Another is recited in the Yotzer ohr blessing, and a third (known as Kedushah d'sidra) is recited on various occasions including the conclusion of weekday Shacharit. In some versions of the kedushah, additional Biblical verses are added in the same format as the verses from Isaiah and Ezekiel.
Amidah
The Kedushah is traditionally the third section of all Amidah recitations. In the silent Amidah it is a short prayer, but in the repetition, which requires a minyan, it is considerably lengthier. The recitation of Kedushah on a daily basis is a Babylonian custom; in classical Israel, the repetition of the Amidah would usually not include Kedushah, with Kedushah added only on special occasions. The liturgy varies among different communities and during different services, but they all hold in common three Bible verses (though translations vary):
Kadosh Kadosh Kadosh Adonai Tz'vaot M'lo Khol Ha'aretz K'vodo
"Holy, Holy, Holy, The Lord of Hosts, The entire world is filled with His Glory."
Baruch K'vod Adonai Mim'komo
"Blessed is the Glory of the Lord in Its Place"
Yimloch Adonai L'Olam, Elohayich Tziyon L'dor Vador Hall'luyah
"The Lord shall reign forever, Your God, O Zion, from generation to generation, Hallelujah"
All three of the verses cited above are recited as part of the congregational response to the cantor. For the first verse, , it is traditional for everyone to rise to their toes with each recitation of the word ('holy').
In the Mussaf services of Shabbat and Festivals, and in some communities in the morning service as well, an enhanced version of the Kedushah is recited, with additional praises in between the biblical verses.