A rehearsal is a dry-run or practice for a future performance. It's just one of many theatrical conventions that Pirandello dissects and playfully subverts in Six Characters in Search of an Author.

The play starts with a a troupe of actors about to perform a rehearsal of a play—also by Pirandello—called The Rules of the Game. But although the rehearsal is then put on hold by the arrival of the six characters of the title, nothing is ever quite what it seems in this play within a play. For one could plausibly argue that everything that happens here on in is nothing more than a rehearsal itself, as the play never becomes—and this is wholly intentional on Pirandello's part—a finished product.

These six unusual characters disrupt proceedings with their own stories, which are then incorporated into the text of the play that the troupe of actors is supposed to be rehearsing. These characters and their stories upend the traditional theatrical rules or conventions as to what constitutes a "well-made play," as indeed does Pirandello is writing Six Characters in Search of an Author.

A knocking-shop is an old-fashioned name for a brothel. In the second act of Six Characters in Search of an Author, two of the characters—the Father and the Step-Daughter—reenact their amorous encounter at Madame Pace's boutique, which turns out to be nothing more than a front for a house of ill-repute.