Hays et al. (1976)
Also: Hays et al. 1976
Variations in the Earth's Orbit: Pacemaker of the Ice Ages
Hays, J. D., Imbrie, J. & Shackleton, N. J. (1976). Variations in the Earth's Orbit: Pacemaker of the Ice Ages. Science. 194(4270),1121-1132. Article
https://doi.org/10.1126/science.194.4270.1121
References
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.