Using ideas, plots, text and other intellectual property developed by someone else while claiming it is your original work. The content in ComputerLanguage.com (this encyclopedia) was placed online in 1997, and although copyright notices are prominently displayed, thousands of definitions have been, and still are, copied to other websites without permission and without adding any reference to the source, typically in quantities from a half dozen to several hundred.
The most interesting copyright infringement of ComputerLanguage.com was a Texas state agency, which copied about a hundred terms to their site years ago and added just one more of their own. The term they added was "plagiarism." True story! See copyright
and Internet piracy