E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
in theatrical slang, means business. Good biz means full houses; but an actors biz is quite another thing, meaning by-play. Thus, Hamlet trifling with Ophelias fan, Lord Dundrearys hop, and so on, are the special business of the actor of the part. As a rule, the business is invented by the actor who creates the part, and is handed down by tradition.