What is Cabal?

Legal Definition
A cabal is a group of people united in some close design together, usually to promote their private views or interests in an ideology, state, or other community, often by intrigue, usually unbeknown to persons outside their group. The use of this term usually carries strong connotations of shadowy corners, back rooms and insidious influence. The term is frequently used in conspiracy theories; some Masonic conspiracy theories describe Freemasonry as an internationalist secret cabal.
-- Wikipedia
Legal Definition
A small association for the purpose of intrigue; an intrigue. This name was given to that ministry in the reign of Charles II. formed by Clifford, Ashley; Buckingham, Arlington, and Lauderdale, who concerted a scheme for the restoration of popery. The initials of these five names form the word "cabal;" hence the appellation. Hume, Hist. Eng. lx. 69.
-- Black's Law Dictionary
Legal Definition
A junto; a small political faction.
-- Ballentine's Law Dictionary