in theatrical slang, means “business.” Good biz means full houses; but an actor's “biz” is quite another thing, meaning by-play. Thus, Hamlet trifling with Ophelia's fan, Lord Dundreary's 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.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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