The following definitions reflect those used by the International Energy Agency (IEA); definitions used by other organisations and publications may vary.


assigned amount unit


active solar thermal

active solar thermal


air-source heat pumps


active solar thermal

advanced vehicles

applies to electric (which are battery powered), plug-in hybrid (which uses two sources of power – most commonly gasoline and electric) and fuel cell models (which convert hydrogen into electricity).

Annex B countries

countries with quantitative targets under the Kyoto Protocol.

Annex I countries

developed countries and countries in transition that have committed under the UNFCCC to undertake emissions reductions activities.


arising from human activity; for example, anthropogenic greenhouse-gas emissions are those linked to human activity rather than natural sources.


an underground water reservoir; if the water contains large quantities of minerals, it is a saline aquifer.


the practice of taking advantage of a price difference between two or more markets.

asset finance

a secured business loan in which the borrower pledges its assets as collateral.

assigned amount unit

the tradable unit under the trading mechanism of the Kyoto Protocol. Each unit allows the country to emit one tonne of CO2 equivalent of any of six greenhouse gases covered by the Protocol.