What is "kedushah"

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 liturgy varies among different communities and during different services, but they all hold in common three lines from the Bible (though translations vary):

קָדוֹשׁ קָדוֹשׁ קָדוֹשׁ ה' צְבָאוֹת מְלֹא כָל הָאָרֶץ כְּבוֹדוֹ 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" (Isaiah 6:3) בָּרוּךְ כְּבוֹד ה' מִמְּקוֹמוֹ Baruch K'vod Adonai Mim'komo "Blessed is the Glory of the Lord in Its Place" (Ezekiel 3:12) יִמְלֹךְ ה' לְעוֹלָם. אֱלֹהַיִךְ צִיּוֹן לְדֹר וָדֹר. הַלְלוּיָהּ 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" (Psalms 146:10)

The Kedushah is enhanced during the morning and Musaf services of Shabbat and Festivals and between the biblical verses there are more praises. The Musaf service of Shabbat and Festivals as well as all of the Kedushahs of Yom Kippur additionally contain the opening line of the Shema.

There is also something called the Kedushah D'Sidrah which is recited at the conclusion of weekday morning services, at the beginning of the afternoon services of Shabbat and Festivals, the conclusion of the evening service of Saturday night, and the beginning of the Neilah service at the end of Yom Kippur. This is different from the Kedushah of the Amidah as it does not require a minyan and it includes an Aramaic recapitulation ( Targum) of the three aforementioned biblical verses of the Kedushah.