Offsetting – The process of reducing carbon emissions by ‘offsetting' it. An example is by taking a flight and in compensation paying a company to plant trees to equal the carbon use out

On-site wastewater treatment - Uses localized treatment systems to transport, store, treat and dispose of wastewater volumes generated on the project site.

Open-grid paving systems - Are a form of pervious paving that allow space for vegetation; the vegetations' evapotranspiration reduces the heat island effect caused by pavement.

Oil – Fossil fuel used to produce petrol etc and other materials such as plastics.

Organic – While it technically refers to molecules made up of two or more atoms of carbon, it's generally now used as a term for the growth of vegetables etc without the use or artificial pesticides and fertilizer.

Ozone layer – In the upper atmosphere about 15 miles above sea level it forms a protective layer which shields the earth from excessive ultraviolet radiation and occurs naturally.