Ice stream
A stream of ice flowing faster than the surrounding ice sheet. It can be thought of as a glacier flowing between walls of slower-moving ice instead of rock.
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.