First publication and definition was:
Riehle, D., Ellenberger, J., Menahem, T., Mikhailovski, B, Natchetoi, Y., Naveh, B., & Odenwald, T. (2009, March/April). Open Collaboration within Corporations Using Software Forges. IEEE Software vol. 26, no. 2, pp. 52-58.
A longer discussion was presented in:
Riehle, D. (2015). The Five Stages of Open Source Volunteering. In Cloud-based Software Crowdsourcing, pp. 25-38. Springer-Verlag.
I picked it up in a couple of blog posts:
I founded and operated, for a while,