General Public Virus
A pejorative name for some versions of the GNU project copyleft or General Public License (GPL), which requires that any tools or application programs incorporating copylefted code must be source-distributed on the same terms as GNU code. Thus it is alleged that the copyleft "infects" software generated with GNU tools, which may in turn infect other software that reuses any of its code.
Copyright law limits the scope of the GPL to "programs textually incorporating significant amounts of GNU code" so GPL is only passed on if actual GNU source is transmitted. This used to be the case with the Bison parser skeleton until its licence was fixed.