What bookdealers really mean. A dictionary by Tom Congalton and Dan Gregory (Between the Covers), with additions from other sources
A pamphlet, book, or broadside, usually ephemeral in nature, made by a mechanical printing or copying process using a stencil. Often seen in amateur printing, or for limited runs of printing, as for instance in screenplays. The stencils would wear out pretty quickly, so these were by their nature a self-limiting process.