A wildfire is ordinarily an uncontrolled fire in the wilderness. Common causes of wildfire are lightning and drought. However, wildfires may also be started by human negligence or arson. They can be a threat to those in rural areas and also wildlife. Wildfires can also produce ember attacks, where floating embers set fire to buildings at a distance from the fire itself.
A prescribed fire becomes a wildfire when an escape has occurred or is likely to occur. Fire outside of the planned perimeter, or outside any planned allowable areas, that cannot be contained with the holding forces identified in the Prescribed Fire Plan, is an escape and will be declared a wildfire.
Wildfire is also termed brush fire, bushfire, forest fire, grass fire, hill fire, peat fire, vegetation fire, veldfire, and wildland fire, depending on the type of vegetation being burned.
The following is an example of a state law (California) defining the term:
"Wildfire" means an unplanned, unwanted wildland fire, including unauthorized human-caused fires, escaped wildland fire use events, escaped prescribed fire projects, and all other wildland fires where the objective is to extinguish the fire. [Cal Gov Code § 51177].