Definition from arXiv:1106.5718:

Due to the high density of neutrinos, self-interaction between neutrinos becomes important and can lead to a range of phenomena called “collective neutrino oscillations” (e.g. Pantaleone 1992; Duan et al. 2006, 2010). In particular, there is a possibility of an instability (Dasgupta et al. 2009) that exchanges part of the high-energy $\nu _x$ spectra with the $\nu _e$ and $\bar \nu _e$ spectra, which may then produce significantly more heating than calculations ne- glecting neutrino oscillations. Chakraborty et al. (2011a,b) and Dasgupta et al. (2011) have investigated the relevance of CνO for the shock revival in the core-collapse simulations of several progenitor models.

REFERENCES
Chakraborty, S., Fischer, T., Mirizzi, A., Saviano, N., & Tomas, R. 2011, arXiv:1104.4031

Chakraborty, S., Fischer, T., Mirizzi, A., Saviano, N., & Tomas, R. 2011, arXiv:1105.1130

Dasgupta, B., O’Connor, E. P, & Ott, C. D. 2011, subm. to Phys. Rev. D, arXiv:1106.1167

Duan, H., Fuller, G. M., Carlson, J., & Qian, Y.-Z. 2006, Phys. Rev. D, 74,105014

Duan, H., Fuller, G. M., & Qian, Y.-Z. 2010, http://arxiv.org/abs/1106.1167