a pressrun, as that of a newspaper or magazine, which is interrupted after the running of a specified number of copies to permit the substitution of type or of a cut, as in a keyed advertisement: a device for testing the relative effectiveness of different versions of an advertisement.
(Canadian) a divided print run of a periodical in which a number of copies contain advertisements not included in the rest, esp a Canadian edition of a US magazine which contains Canadian advertisements but no Canadian editorial content
