Attributive relating to or designating thick black marks printed at progressively differing positions on the fold of the outer leaf of each section, and used as a guide to collating the sections in the correct order for binding.
Origin
1940s.
Definition of black-step in US English:
black-step
noun
Printing
Attributive relating to or designating thick black marks printed at progressively differing positions on the fold of the outer leaf of each section, and used as a guide to collating the sections in the correct order for binding.