I'm going to attempt this in a paragraph. It's an outsider's summary, but I've found the subject interesting enough to have read nearly two hundred books on the subject, though only a few in Hebrew.
Spelled Qoph Beth Lamed He or QBLH, the word refers to a "received tradition." The tradition includes: a) A large collection of mystical teaching stories; b) A system of Biblical and Talmudic exegesis, largely based on alphabet mysticism and numerology; c) A system of correlative thought, particularly using the scales and patterns of three, four, seven, ten, twelve, twenty-two and thirty-two; d) An ontological model of the process of creation that is also, in its inverse form, a program of spiritual evolution. The tradition is about eight centuries old, but it wraps itself in a much longer, bogus history to attract its more gullible believers. It also reaches back in time from its beginning to capture a small text, the Sefer Yetzirah, that may be as old as the 6th century, and borrows what I believe to be two Song Dynasty Chinese diagrams, called Wujitu and Taijitu, brought to Europe by the Arabs, renaming their ten spheres after certain characteristics of their own deity enumerated in the Jewish Bible. It retroactively makes these into fundamental components of its system. The system of belief bears at least as much resemblance to Gnosticism as to Judaism, and differs from Judaism most in its beliefs in an impersonal deity, En Sof (the Unlimited), reincarnation, spiritual evolution and redemption. The deity also has an important feminine aspect, named the Shekinah. The Jewish system has a much more open and eclectic Western European or Hermetic counterpart, which it scorns unnecessarily, as a people with such delusions of grandeur as to think themselves the favored children of the creator of the universe must believe of anything not wholly their own. It is deeply paranoid in this and other respects. Kabbalah's weakest feature is its a priori assumption that the Jewish Bible contains significant quantities of religious truths that are deeply buried, and that this is a primary locus of truth. Alleged historical connections to the Tarot are specious at best, but a significant amount of co-evolution has occurred in recent centuries, and the QBLH models of the scales of four and ten, as number archetypes, particularly as developed in the Hermetic QBLH, have much to offer towards an understanding of the Tarot's numbers and suits. The assignment of the Tarot's trumps to the 22 letters of the Hebrew alphabet relies heavily on the assumption of a metaphysical significance to the linear sequence of that alphabet, which some of us with mental faculties still intact might regard as a bunch of hooey. But this does not prevent us from playing productive Glass Bead Games between the two systems.