Hebrew for "Tradition" 

Modern academic study of Jewish mysticism usually uses this term for the type of mystical teachings & practices based on the Zohar ("Splendor"), a collection published by the 13th c. Spanish rabbi Moses de Leon. But the Zohar was a synthesis of ideas embedded in earlier esoteric Jewish texts that represent more than a millennium of rabbinic speculation on the interpretation of certain cryptic passages in Hebrew scripture & apocalyptic apocrypha. 

Meditation on biblical accounts of creation (Gen 1), visionary experiences (e.g., Isaiah 6 & Ezekiel 1) & heavenly ascents (e.g., Enoch & Elijah), led early Jewish mystics to develop & refine ever evolving descriptions of the heavenly "palaces" (Hekhaloth), throne chariot of God (Ma'aseh Merkabah) & status of the human in creation (Ma'aseh Bereshit^h).  Since some speculation on these topics led to conclusions deemed dangerous by the rabbinic academy (e.g., the "Two Powers" controversy), public reading & discussion of these passages of scripture was restricted by the early 2nd c. CE.

Yet continued interest in these esoteric topics led to composition & circulation of a wide array of texts intended for private use, some of which were later collected into compilations attributed to eminent rabbis who flourished prior to the public ban (e.g., Aqiba ben Joseph, Ishmael ben Elisha & Simeon ben Jo^chai).  Unlike scripture & Talmud, the content of these early kabbalist texts was fluid & not fixed. A given text was not just transmitted as received but was subject to expansion & revision incorporating personal insights of the anonymous scribe who copied it. Thus these texts testify to the evolution of Jewish mystical thinking prior to publication of the Zohar, that may collectively be called proto-kabbalah.

Examples of proto-kabbalah included in this sourcebook are two expositions of an acrostic based on aleph, the first letter of the Hebrew alphabet, which Jewish mystics regarded as the source of the cosmos created by God speaking. The first is a fragment appended to one copy of the Ma'aseh Bereshit^h; the second, from a fragment appended to Sepher Heno^ch (the Hebrew "Book of Enoch,") which today is usually referred to as 3 Enoch to distinguish it from apocalypses of the same name which have survived only in Ethiopic (1 Enoch) and old Slavonic (2 Enoch).  While experts trace the finished compilations to the 5th c. CE, these fragments are arguably older than the works to which they were appended.

Other resources on line:

• Kabbalah - overview in Wikipedia's web.

• Cabala - comprehensive index to the history, works, and major topics of Judaic kabbalah  (Jewish Encyclopedia).

• All the  Books of Enoch - digital edition of English versions of the Ethiopic, Slavonic & Hebrew works so-named includes Hugo Odeberg's translation of 3 Enoch (Internet Archive).  

• Merkabah mysticism - survey of the history & literature of the first millennium of Jewish mysticism (Wikipedia).