A split or divergence in the source code.
When SourceCode is forked, two or more groups, with different visions, develop the code to their own ends. The NetworkEffect is a powerful deterient to forking, since halving the number of developers working on the source for a project move than halves the productivity of each group. In most cases all but one of the forks eventually withers and dies, ironically leaving the remaining fork with a much more clearly defined vision.
Well-known examples include
See also OpenSource