Canovaccio was mainly used in the Commedia dell'Arte and consisted of the disposition of acts and scenes: a vague plot, and not much more. The details were left to the improvisation of the actor. Thus actors in the Commedia dell'Arte had to be endowed with an inventive mind since success of the play depended largely on the actor's interpretive ability, creativity, and acting, and above all on his lazzi - his jokes and gags. The spotlight fell on the actors rather than on the play itself.
The use improvisation on top of canovaccio enabled the avoidance of censorship. Censors cannot censor that which is not written. Since everything was almost entirely improvised on stage, actors and theatre companies could get away with almost anything.
In the Commedia dell'arte it was an outline of entrances, exits, and action describing the plot of a play that was literally pinned to the back of the scenery.
It is also known as canovaccio or "that which is pinned to the canvas" of which the scenery was constructed.
Surviving scenari from the renaissance contain little other than character names, brief descriptions of action, and references to specific lazzi with no further explanation.