Ashcan

Historically - An ashcan comic is a comic produced solely to establish a publication date for copyright purposes. Most of the times these sent to the 'Ashcan' to be destroyed but some survived in some cases. These were not distributed and only a few copies were ever made

This term can also be used to describea mock up for a new title proposition.

An ashcan can also refer to a promotional only comic, or one sold cheaply as an introduction to a new title