From 2D Market:
Copy books or Kopihons are small, few pages long doujinshi that are usually sold for a small price at doujinshi conventions alongside their bigger cousins. They got their name from the fact that they are usually photocopied rather than properly printed.
This doujinshi collects five Kabayakiya Kopihons that were originally published between January 2012 and February 2013. Each of the five part is 4 pages long, with 3 pages of manga and one full-page illustration.
Source: Various (Haganai, Rinne no Lagrange, AnoNatsu, iM@S, SAO)