A weed is any plant that requires some form of action to reduce its effect on the economy, the environment, human health and amenity. Weeds are also known as invasive plants or plants that are growing in the wrong place at the wrong time. Many plants that have been introduced into Australia as ornamental or garden plants in the last 200 years are now weeds.

Weeds typically produce large numbers of seeds which assist in their ability to spread and have many unfavorable tendencies characteristics, such as long seed life, ease of spread and are usually hard to control.  Most are excellent at surviving, adapting and reproducing either in areas with favorable weather conditions or in disturbed or hostile environments. 

A weed can be an exotic species or a native species that colonizes and persists in an ecosystem in which it did not previously exist. Weeds can inhabit all environments; from our towns and cities through to our oceans, waterways, forests, deserts and alpine areas.

Some weeds are of particular concern and as a result, are declared Noxious Weeds due to their detrimental impact on human health, agriculture and/or our environment.

A range of management frameworks have been developed to help coordinate the management of weeds at different levels of government throughout Australia including the NSW Noxious Weed Act, Invasive Species Plan, Regional Weed Management Plans and Strategies. Also a list of Weeds of  National Significance has been developed.