Drama is the Greek word for action, and so, in a play, what the people do is even more important than what they say. Practically every motion made on the stage, except that of walking, comes under the head of what is known technically as "business." Laymen who believe that mummers act on their own initiative, even "making up" lines as they go along, will be surprised to learn that the manuscript of a workmanlike play contains more "business" than dialogue. The performer picks up a photograph or lights a cigar or toys with a riding whip, not because it has occurred to him to do so, but because the author has written down what he must do, and how and when he must do it, and the stage director has taught him properly to interpret the author.
Here is a page from the "prompt copy" of "Clothes." The unbracketed sentences are dialogue; those in parenthesis are "business":
WEST.
I'm going to marry you in spite of——
(Checks himself suddenly. Gets his hat and brushes it with his sleeve. Laughs a little.)
Pardon me. My temper is a jack-in-the-box. The cover is down again. Goodnight.
(Walks quickly to door L. C., and exits. OLIVIA stands still a moment, then throws herself into chair R. of table, and indulges in a torrent of tears. The bell rings. She sits upright and listens. It rings again. She rises and runs to door L. 2. E. The MAID enters.)
The capital letters—L. C., R., and L. 2. E. are abbreviations of terms that indicate exact spots on the stage. You see, it is not left to the discretion of West by which door he shall leave the room, nor of Olivia into which chair she shall throw herself. This "business" the director works over at rehearsal, elaborating, amplifying, making clear. West is told precisely where he must find his hat, with which arm he must brush it, in what tone he must laugh. If this were a case where a pause would heighten the effect of an entrance, the maid would be informed, as was the mythical Mr. Leeds in my opening paragraphs, how many she must count, which is to say how long she must wait, before entering.
The more experienced an author, the more definite, exhaustive and significant his "business." When a play goes into rehearsal, however, there are always places where speech may be exchanged for action, and often, after a dramatist has seen his work on the stage, he is able to cut whole pages, the sense of which is made clear by the appearance, the manner, or the "business" of his people.