Glossary: O

Here you will find definitions of terms used in resources on the Foodsource website. You will also find these definitions on the right-hand side within chapters. If you have any suggestions for new glossary items, let us know here.

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Organic farming

is an approach to farming in which synthetic chemical insecticides and herbicides and inorganic fertilisers are entirely or largely avoided. Underpinning organic farming is the idea that farming should rely on ecological processes, biodiversity and cycles adapted to local conditions, rather than the use of inputs with adverse effects (e.g. agrochemicals such as pesticides and synthetic fertilisers). Certification bodies (e.g. the Soil Association in the United Kingdom) specify the practices, methods of pest control, soil amendments and so forth that are permissible if products are to achieve organic certification.


Excesses of energy or a particular nutrient. Overnutrition generally refers to excessive intake of energy, but it can sometimes be used to refer to excessive intake of one or more other dietary components such as specific macronutrients or micronutrients. Overnutrition in terms of energy often results in being overweight or obese.


A molecule consisting of three oxygen atoms (chemical formula O3; ‘trioxygen’). In the upper atmosphere (‘stratosphere’) ozone plays an important role in absorbing ultraviolet radiation from the sun, but is also a greenhouse gas, and at the surface has negative impacts on human health and plant growth. Ozone is also one of the by-products from atmospheric methane oxidation.

Ozone layer depletion

A decline in the level of ozone gas (O3) present in the earth's stratosphere, owing to its breakdown into oxygen (O2). This breakdown can be affected by natural processes, but is known to have been accelerated by the release of man-made chemicals, such as refrigerant gases. The ozone layer acts to reduce the amount of light at ultra-violet wavelengths reaching the earth's surface; wavelengths that can have harmful impacts on humans, including skin cancer.