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)
  1. A description of a desired condition; quantified and measured, and where possible, with established time frames for achievement.
  2. Specific, achievable, measurable, time-limited results to be achieved through land management practices, either through a description of a desired condition or the degree of desired change in an attribute. 
Observation Time
  • Time of day required to record meteorological data at a fire danger station. 
Obstruction to Vision
  • Condition in which obscuring phenomenon restricts horizontal visibility to six statute miles (10 km.) or less. 
Occluded Front or Occlusion
  • The front that is formed when and where a cold front overtakes a warm front or a stationary front. 
Occurrence Index (OI)
  • A number in the National Fire Danger Rating System related to potential fire incidence within a protection unit. 
Off-road Vehicle (ORV)
  • Any motorized vehicle designed for, or capable of, cross-country travel on or immediately over land, water, sand, snow, ice, marsh, swampland, or other terrain. 
  • Non-compensable time, e.g., eating, sleeping or other activities of a personal nature.
Off-Site/Remote Assignment
  • Work performed by an individual employee in support of an incident while remaining at the employee’s duty station or other designated off-site location.
  • The ICS title for personnel responsible for the Command Staff positions of Safety, Liaison, and Information. 
Offshore Flow
  • Wind blowing from land to water. 
  • Status of a federal casual or federal regular government employee used for timekeeping purposes. An employee will be considered off duty and time spent in an on-call status shall not be considered hours of work if: 1) The employee is allowed to leave a telephone number or to carry an electronic device for the purpose of being contacted, even though the employee is required to remain within a reasonable call-back radius; or 2) The employee is allowed to make arrangements such that any work which may arise during the on-call period will be performed by another person. (Reference 5 CFR 551.431(b) (1-2)). Specific state pay guidelines for non-pay status shall apply for state employees.
  • Time of actual work, ordered standby, or compensable travel with a specific start and ending time.
One Lick Method
  • A progressive system of building a fireline on a wildfire without changing relative positions in the line. Each worker does one to several "licks", or strokes, with a given tool and then moves forward a specified distance to make room for the worker behind.
One-hour Timelag Fuel Moisture (1-h TL FM)
  • Moisture content of one-hour timelag fuels. 
One-hour Timelag Fuels
  • Fuels consisting of dead herbaceous plants and roundwood less than about one-fourth inch (6.4 mm) in diameter. Also included is the uppermost layer of needles or leaves on the forest floor. 
One-hundred Hour Timelag Fuel Moisture (100-h TL FM)
  • The moisture content of the 100-hour timelag fuels. 
One-hundred Hour Timelag Fuels
  • Dead fuels consisting of roundwood in the size range of 1 to 3 inches (2.5 to 7.6 cm) in diameter and very roughly the layer of litter extending from approximately three-fourths of an inch (1.9 cm) to 4 inches (10 cm) below the surface. 
One-thousand Hour Timelag Fuel Moisture (1,000-h TL FM)
  • The moisture content of the 1,000-hour timelag fuels. 
One-thousand Hour Timelag Fuels
  • Dead fuels consisting of roundwood 3-8 inches in diameter and the layer of the forest floor more than about 4 inches below the surface. 
Onshore Flow
  • Wind blowing from water to land. 
Open Burning
  • Burning of any fuel outdoors without the use of mechanical combustion enhancements. 
Open Line
  • Refers to open fire front where no line has been constructed. 
Operating Weight
  • For helicopters, the equipped weight plus weight of the crew and fuel. 
Operational Control
  • The exercise of authority over initiating, conducting, or terminating any operation. Often associated with aviation operations. 
Operational Period
  • The period of time scheduled for execution of a given set of tactical actions as specified in the Incident Action Plan. Operational Periods can be of various lengths, although usually not over 24 hours. 
Operational Tempo
  • The speed and intensity of actions relative to the speed and intensity of the unfolding events in the operational environment. 
Operations Coordination Center (OCC)
  • Primary facility of the Multi-agency Coordination System (MACS); houses staff and equipment necessary to perform the MACS function. 
Operations Section
  • The section responsible for all tactical operations at the incident. Includes branches, divisions and/or groups, task forces, strike teams, single resources and staging areas. 
  • A circular holding pattern of an aircraft around a fixed location often related to a wildland fire. For example, the circular pattern of an airtanker in the vicinity of a wildland fire, waiting to make a retardant drop. 
Ordered Standby
  • An employee is on duty, and time spent on standby duty is hours of work if, for work-related reasons, the employee is restricted by official order to a designated post of duty and is assigned to be in a state of readiness to perform work with limitations on the employee’s activities so substantial the employee cannot use the time effectively for his or her own purposes. A finding that an employee’s activities are substantially limited may not be based on the fact that an employee is subject to restrictions necessary to ensure that the employee will be able to perform his or her duties and responsibilities, such as restrictions on alcohol consumption or use of certain medications (5 CFR 551.431(a) (1)).
Organic Matter
  • That fraction of the soil that includes plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by the soil population. 
Organic Soil
  • Any soil or soil horizon containing at least 30% organic matter (e.g., muck, peat). 
  • Pertaining to, or caused by mountains. 
  • Photograph obtained from the orthogonal (i.e., horizontal) projection of a correctly oriented stereoscopic model formed by two overlapping aerial photographs; an orthophoto is free of tilt and relief displacements. 
Orthophoto Maps
  • Aerial photographs corrected to scale such that geographic measurements may be taken directly from prints. They may contain graphically emphasized geographic features and may be provided with overlays of such features as: water systems, facility location, etc. 
Osborne Firefinder
  • A sighting device used by lookouts to determine the horizontal bearing and sometimes the vertical angle of a fire from a lookout. 
Other Training Which Supports Development of Knowledge and Skills
  • Courses defined as containing supplemental knowledge and skills not required for safe and tactical operations success on a wildfire.
    • Synonym: Recommended Training
Out-of-Service Resources
  • Resources assigned to an incident but unable to respond for mechanical, rest, or personal reasons. 
Outside Aid
  • Firefighting assistance given to adjacent areas and nearby communities by contract or other agreement that covers conditions and payment for assistance rendered and services performed. Contrasted to mutual aid, in which neighboring firefighting organizations assist each other without charge. 
Outside Diameter (OD)
  • External diameter of a cylinder or tube, conductor, or coupling as distinguished from the internal diameter. 
  • Fire department procedure of inspecting premises after extinguishment of fire, to insure that fire is completely out and unable to rekindle before returning control to owner or occupants. 
  • Personnel assigned to supervisory positions, including incident commander, command staff, general staff, branch directors, supervisors, unit leaders, managers and staff. 
  1. Gross vehicle weight (GVW) in excess of the gross vehicle weight rating (GVWR) specified by the chassis manufacturer. Also an excess of weight over the gross vehicle axle weight rating (GAWR) specified by the chassis manufacture.
  2. A situation that taxes an operational system to the limit of its functional capabilities. Such as too many fires for an individual unit to handle (fire overload), or too many orders for an individual dispatch center to process (dispatch overload). 
Overwintering Fire
  • A fire that persists through the winter months until the beginning of fire season. 
  • Process during which oxygen combines with another substance. 
  • The portion of a chemical mixture or compound which furnishes oxygen for burning a fuel or propellant, creating an oxide.