The Chayot or Hayyoth are a class of Merkabah

Merkabah

Merkabah is the throne-chariot of God, the four-wheeled vehicle driven by four "chayot" , each of which has four wings and the four faces of a man, lion, ox, and eagle...

, or Jewish Mystical Angel

Angel

Angels are mythical beings often depicted as messengers of God in the Hebrew and Christian Bibles along with the Quran. The English word angel is derived from the Greek ἄγγελος, a translation of in the Hebrew Bible ; a similar term, ملائكة , is used in the Qur'an...

, reported in Ezekiel

Ezekiel

Ezekiel , "God will strengthen" , is the central protagonist of the Book of Ezekiel in the Hebrew Bible. In Judaism, Christianity and Islam, Ezekiel is acknowledged as a Hebrew prophet...

's vision of the Merkabah and its surrounding angels as recorded in the first chapter of the Book of Ezekiel

Book of Ezekiel

The Book of Ezekiel is the third of the Latter Prophets in the Hebrew Bible, following the books of Isaiah and Jeremiah and preceding the Book of the Twelve....

 describing Ezekiel's vision by the river Chebar.

Chayot are ranked first on Maimonides

Maimonides

Moses ben-Maimon, called Maimonides and also known as Mūsā ibn Maymūn in Arabic, or Rambam , was a preeminent medieval Jewish philosopher and one of the greatest Torah scholars and physicians of the Middle Ages...

' Jewish angelic hierarchy

Jewish angelic hierarchy

Maimonides, in his Yad ha-Chazakah: Yesodei ha-Torah, counts ten ranks of angels in the Jewish angelic hierarchy, beginning from the highest:- Kabbalistic angelic hierarchy :...

.

In Judaism

In Judaism the Chayot are considered angels of fire, who hold up the throne of God and the earth itself. (and would therefore be on the same level as the Christian Seraphim) and residing in the Seventh heaven.