NWCG Glossary of Wildland Fire, PMS 205

This glossary provides the wildland fire community a single source for wildland fire and incident management terminology commonly used by the NWCG and its subgroups.

Glossary entries related to Organizations, IT Applications, and NWCG Positions have been removed from the glossary based on term inclusion criteria. For more information about the glossary and the criteria, see the About the NWCG Glossary page or the NWCG User Guide for the Glossary of Wildland Fire, PMS 937.

Reference Definitions

Some of the terms within this glossary will be followed by initials or will have references or comments at the end of the definition to help broaden the recognition and understanding of the term. An explanation of those references is as follows:

Also called: Means there is another term that may sometimes be in use, but is not defined in this glossary.
Acronym: An abbreviation formed from the initial letters of other words and pronounced as a word. An acronym appears in parentheses following the term.
Initialism: An abbreviation consisting of initial letters pronounced separately. An initialism appears in parentheses following the term.
See: Means there is another, preferred term that should be used instead. In such a case only the preferred term is defined in this glossary.
See Also: Means there are one or more related terms that may also be of interest to the glossary user. The related terms are also defined in this glossary.
Synonym: Means the term is synonymous with another. The terms have the same, or essentially the same, definition and the terms are interchangeable in their use.
Definition Extension: An example, further explanation, or usage guidance in support of the definition.

Glossary Acronyms/Initialisms

6 (1) | A (126) | B (94) | C (160) | D (102) | E (67) | F (261) | G (48) | H (90) | I (83) | J (10) | K (4) | L (74) | M (92) | N (31) | O (47) | P (133) | Q (6) | R (100) | S (221) | T (71) | U (28) | V (37) | W (60) | Z (1)
V Pattern
  • Characteristics fire cone-shaped pattern left by a fire on a wall, at or near its point of origin. 
Values at Risk
  • The elements of a community or natural area considered valuable by an individual or community that could be negatively impacted by a wildfire or wildfire operations. These values can vary by community and can include diverse characteristics such as homes, specific structures, water supply, power grids, natural and cultural resources, community infrastructure, and other economic, environmental, and social values.
Values To Be Protected
  • Include property, structures, physical improvements, natural and cultural resources, community infrastructure, and economic, environmental, and social values. 
Vapor Suppression
  • Creating a seal with foam which prevents a release of flammable vapors from fuels. 
  • Any changing characteristic; in statistics, a measurable characteristic of an experimental unit. 
Variable Ceiling
  • A ceiling of less than 3,000 feet (900 m) which rapidly increases or decreases in height by one or more reportable values during the period of observation. 
Variable Danger
  • Resultant of all fire danger factors that vary from day to day, month to month, or year to year (e.g., fire weather, fuel moisture content, condition of vegetation, variable risk) 
Variable Sky Condition
  • A sky condition that varies between reportable values of sky cover amounts during the period of observation. 
Variable Visibility
  • A condition when the prevailing visibility is less than 3 miles (5 km) and rapidly increases and decreases by one or more reportable values during the period of observation. 
Variable Wind Direction
  • Wind direction which varies by 60 degrees or more during the period of time the wind direction is being determined. 
  • Directions of fire spread as related to rate of spread calculations (in degrees from upslope). 
Vegetative Regeneration
  • Development of new aboveground plants from surviving plant parts, such as by sprouting from a root crown or rhizomes. Even if plants form their own root system, they are still genetically the same as the parent plant. 
Vegetative Reproduction
  • Establishment of a new plant from a seed that is a genetically distinct individual. 
Vehicle Fire
  • Fire originating in or on a vehicle or mobile equipment. 
  • The release of enclosed smoke and heat from a structure by creating openings in it, as by hacking a hole in the roof, to allow free passage of air. 
Ventilation Factor
  • A numerical value relating the potential of the atmosphere to disperse airborne pollutants from a stationary source, calculated by multiplying the mixing height by the transport wind speed. 
Ventilation Index
  • A measure of the volume rate of horizontal transport of air within the mixing layer, per unit distance, normal to the wind. Units are measured in square meters per second or knot-feet. 
Vertical Fuel Arrangement
  • Fuels above ground and their vertical continuity, which influences fire reaching various levels or vegetation strata. 
Vertical Temperature Profile
  • Plot of the actual dry-bulb temperature against height above the earth's surface, most commonly determined by a RAWINSONDE observation. 
Very High Frequency (VHF-AM)
  • Radio frequency range from 30 MHz to 299 MHz. The sub-bands most commonly used by fire are:
    • VHF-FM Lo band: Frequency Modulation 30 MHz - 80 MHz, of which fire frequencies are between 30 MHz and 50 MHz.
    • VHF-FM Hi band: Frequency Modulation 150 MHz - 174 MHz. This is the most widely used band by fire agencies.
    • VHF-AM: Amplitude Modulation. This band is commonly referred to as the "Victor or VHF" band. The frequency range is from 118 MHz to 136 MHz. The only authorized use of this band is for aviation. The FAA controls and assigns all frequencies within this sub-band. 
VHF Omnidirectional Radio Range (VOR)
  • System of radio navigation in which any magnetic bearing relative to a special radio transmitter on the ground may be chosen and flown by an aircraft pilot. 
  • A subjective assessment of the health of individual plants in similar site and growing conditions; or a more specific measure based upon a specific facet of growth, such as seed stalk or tiller production per plant or per unit area. 
  • Thickness of a liquid, the degree to which it resists flow. 
Viscous Water
  • Water that contains a thickening agent to reduce surface runoff; tends to cling to burning fuels and spread in layers that are several times thicker than plain water, thereby having an increased capacity to absorb heat, cool fuel, and exclude oxygen. Also known as thickened water. 
Visual Flight Rules Conditions (VFR)
  • Basic weather conditions prescribed for flight under Visual Flight Rules: ceiling above 1,000 feet (300 m) and flight visibility in excess of 3 miles (5 km). 
Visual Greenness (VG)
  • An NDVI-derived image of vegetation greenness compared to a very green reference such as a golf course. 
Visual Range
  • Maximum distance at which a given object can just be seen by an observer with normal vision. 
Visual Resource Management (VRM)
  • The inventory and planning actions taken to identify visual values and to establish objectives for managing those values; and the management actions taken to achieve the visual management objectives. 
Visual Resources
  • The visible physical features on a landscape (e.g., land, water, vegetation, animals, structures and other features). 
Visual Search
  • A systematic and thorough scan of the wildland fire environment for an object or feature as it relates to seeing or sight. This scan may be aided by magnification when necessary.
  • Readily changeable into vapor at low temperatures. 
  • Readily vaporized organic materials which, when mixed with oxygen, are easily ignited. 
Volunteer Fire Department (VFD)
  • A fire department of which some or all members are unpaid. 
Volunteer Firefighter
  • Legally enrolled firefighter under the fire department organization laws who devotes time and energy to community fire service without compensation other than Worker's Compensation or other similar death and injury benefits. 
Vortex Turbulence
  • Miniature whirlwinds trailing from the wingtips of any aircraft in flight. Vortex will be in the form of a horizontal whirlwind with velocities up to 25 mph (40 km) per hour or more. Also created by action of rotor blades on helicopters; these whirlwinds tend to move downward toward the ground. If an aircraft flies low over a fire, vortices may reach the ground and suddenly cause violent and erratic fire behavior.