(Limelight). Do you know what a gimbal stage is, or a gaffer? What is the Alexander technique? And what does it mean when a director says, ''Back to one!'' or ''Stop thinking!''? Does a film director want a piece of fruit when he or she asks for a half apple, or says, ''Give me a banana!''? Do you know what a soundie is? (No relation to a techie!) All these terms and countless more are defined in the remarkable Blumenfeld's Dictionary of Acting and Show Business . Author Robert Blumenfeld combines his expertise from years of working in show business with meticulous research to present a work that is comprehensive and user-friendly. This complete reference book on the art, craft, and business of entertaining is a must-have for every fan, teacher, student, amateur, and professional. Oh, and a half apple? Well, an ''apple box'' is an eight-inch high wooden platform an actor stands on to appear taller. (The term dates to the silent film era when an actual fruit crate was used.) A ''half-apple'' is four inches tall - half the height of an apple box. But when a film director says ''Give me a banana,'' she's telling the actor to walk in front of the camera in a smooth, gentle curve, as if he were tracing the shape of a banana on the floor. (Of course, in vaudeville slang, a ''banana'' is a comedian, and his sidekick is a ''second banana.'') All these entries and 4000 more are defined, including slang, idioms, acronyms, historical terms, common expressions, and legal language in Blumenfeld's Dictionary of Acting and Show Business.