Pleistocene
The earlier of two Quaternary epochs, extending from the end of the Pliocene, about 1.8 million years ago, until the beginning of the Holocene about 11,600 years ago.
Definition courtesy of IPCC AR4.
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.