Acid rain: The name commonly given to the deposition of a mixture of acidifying compounds to soils, surface waters and buildings from the atmosphere. These compounds are initially released to the atmosphere as gases, mainly sulphur dioxide and nitrogen oxides but also hydrogen chloride, which combine with water to form sulphurous, sulphuric, nitrous, nitric and hydrochloric acids. They are derived from a number of sources, including power stations, industrial combustion processes, road transport and waste incineration.

Best management practice (BMP): Methods that have been determined to be the most effective, practical means of preventing or reducing pollution from non-point sources.

Best practicable environmental option (BPEO): This concept was originally recommended by The Royal Commission on Environmental Pollution and introduced by the Government. The Royal Commission itself stated that "a BPEO is the outcome of a systematic and consultative decision-making procedure, which emphasises the protection and conservation of the environment across land, air and water. The BPEO procedure establishes, for a given set of objectives, the option that provides the most benefits or the least damage to the environment as a whole, at acceptable cost, in the long term as well as in the short term".

Biodiversity: The variety of animals, plants, fungi and micro-organisms that inhabit a place is its biodiversity.

Brundtland Commission: The informal name for the World Commission on Environment and Development (WCED), established in 1984 by the UN General Assembly, and chaired by Norwegian Prime Minister Gro Harlem Brundtland. In its report Our Common Future (1987), the commission popularised the idea of sustainable development through global co-operation.

Carbon tax (also known as the energy tax): According to the DETR's A Summary of the Response to the Climate Change Consultation (August 1999) there was "a difference of opinion about an energy/carbon tax. Environmental groups and local authorities thought that a tax could help reduce emissions. However, most businesses were concerned that it might affect their competitiveness".

Chlorofluorocarbons (CFCs): Compounds containing chlorine, fluorine and carbon. The compounds generally are used as propellants, refrigerants, blowing agents (for producing foam) and solvents. The compounds are inert, non-toxic and easily liquefied chemicals implicated in two major environmental problems: ozone-layer depletion and global warming.

Closed loop: This is a system that recycles materials and resources back into the production process, without any emissions of toxic materials.

Critical load: This is defined as "a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge".

Deforestation: This refers to the loss of forest. The adverse effects of deforestation include: the loss of habitat for countless animal and plant species; the destruction of the homes and livelihoods of native tribes; providing an easy path for soils to wash away and rain to flood valleys below; and the addition of carbon dioxide to the atmosphere.

Eco-efficiency: It combines environmental and economic performance to create more value with less impact.

Effluent: Anything that flows out of a pipe, smokestack (which is emissions from stacks or chimneys), storage tank, channel, or sewer.

Ecosystem: The basic functional unit in ecology; the interacting system of a biological community and its non-living environmental surroundings. These are inseparable and act upon each other.

Emissions trading: This scheme was recommended by Lord Marshall's Taskforce during 1998 in its report to the Chancellor of the Exchequer. Emissions Trading and an energy tax were recommended for further exploration by the Taskforce as possible tools to help the UK to meet its greenhouse gas reduction targets. Following on from the work of the taskforce, it has recently been made clear that the Government is taking forward Lord Marshall's recommendation to set up an emissions trading scheme to complement the Climate Change Levy. CBI and ACBE are to pilot a UK trading scheme. Emissions trading is intended to be used as part of energy efficiency targets for those firms involved in negotiated agreements.

Endocrine disrupter: Chemicals which mimic hormones. At present, there is particular concern about these `endocrine disrupters' and the UK is working with other countries to gauge the extent of any problems.

Environment: The sum of all external conditions affecting the life, development, and survival of an organism in a broader context. It also relates to such matters as people's health and pollution.

Environmental measures: Steps taken by an entity or, on its behalf, by others, to prevent, reduce or repair damage to the environment or to deal with the conservation of resources.

Fertilisation effect: A feedback mechanism in which increased atmospheric C0{-2} increases the growth of plants, enhancing their ability to absorb C0{-2}.

Global warming: This term is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing the earth's surface temperature to rise.

Grey zone costs: These refer to costs that are not solely or clearly 'environmental' in nature but may also be viewed, in whole or part, as health and safety costs, risk management costs, production costs, operational costs, and so on.

Green energy: The energy that is produced and used in ways that produce less air pollution and other environmental impacts. Green energy provides two kinds of benefits: i) reduces environmental impacts of production and delivery of the energy we use; and ii) reduces the environmental emissions from the energy we use.

Green Revolution: This relates to an organised effort beginning in the 1960s, sponsored by the United Nations Food and Agricultural Organisation (FAO), to increase world food production by introducing high-yield cereal varieties developed in the Philippines and Mexico.

Greenhouse effect: The warming of the Earth's atmosphere attributed to a build-up of carbon dioxide or other gases.

Greenhouse gases: The trace gases which contribute to the greenhouse effect.

Life cycle of a product: This means all stages of a product's development, from extraction of fuel for power to production, marketing, use, and disposal.

Light pollution: The popular name for sky glow - a brightening of the night sky caused by the scattering of artificial light by aerosol particles (for example, water droplets and fine particles) in the air. Since the 1950s, an increase in the use of artificial lighting has reduced our ability to view the night sky. Light pollution also includes the intrusion of light directly (for example, a bright street light outside a bedroom window).

Ozone (0{-3}): A molecule made up of three atoms of oxygen. In the stratosphere, it occurs naturally and it provides a protective layer shielding the earth from ultraviolet radiation and subsequent harmful health effects on humans and the environment. Ozone is poisonous.

Ozone depletion: The destruction of the stratospheric ozone layer which shields the earth from ultraviolet radiation harmful to life. Ozone hole: A thinning break in the stratospheric ozone layer. Designation of amount of such depletion as an "ozone hole" is made when the detected amount of depletion exceeds 50 per cent.

Ozone layer: The protective layer in the atmosphere, about 1 5 miles above the ground, that absorbs some of the sun's ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the earth's surface.

Risk assessment: A technique that helps identify and measure the nature and magnitude of environmental risk of an organisation's activities on the natural environment. It includes the impact on the health and safety of people and the potential legal and business exposure affecting the organisation.

Social costs: Can be a synonym for `societal costs' or a subset of `external costs'. 'Social costs' are the costs of a company's impacts on the environment and society for which the business is not financially responsible.

Voluntary costs: These represent costs incurred by a company that are not required or necessary for compliance with environmental laws but go beyond compliance. For example, this may include donations to outside environmental projects.

Smog: The DETR classifies this into both winter smog and summer smog. The latter is caused by a mixture of pollutants from: i) road vehicles, ii) fuels used to provide electricity and heating in offices, factories and homes, and iii) vapours from petrol and certain industrial premises. Summer smog is formed by the action of sunlight on these pollutants which forms low-level ozone close to the ground. Winter smog is caused by a mixture of pollutants from: a) road vehicles, and b) fuels used to provide electricity and heating in offices, factories and homes.
Winter smog is formed by pollutants at ground level in urban areas. The `lid' of cold air above the warm air then traps the pollutants.

Toxic air pollutants: These are poisonous substances in the air that come from natural sources (for example, radon gas coming up from the ground) or from man-made sources (for example, chemical compounds given off by factory smokestacks) and can harm the environment and health. Triple bottom line: This involves integrating action and setting priorities to improve business performance on economic, environmental and social aspects.

Wetlands: An area that is regularly saturated by surface water or groundwater and subsequently characterised by a prevalence of vegetation that is adapted for life in saturated-soil conditions.