LTNGLightning- A visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between the cloud and air, between…
Lubricant(LOO-brih-kant) An oily or slippery substance.
LumenThe cavity or channel within a tube or tubular organ such as a blood vessel or the intestine.
Lumens/Watt (lpw)A measure of the efficacy (efficiency) of lamps. It indicates the amount of light (lumens) emitted by the lamp for each unit of electrical power (Watts)…
LuminaireA complete lighting unit consisting of a lamp(s), housing, and connection to the power circuit.
LuminanceThe physical measure of the subjective sensation of brightness; measured in lumens.
LuminosityThe total energy released by an object emitting light, (in our case, this will be a star) per unit time (usually per second).
luteinizing hormoneA pituitary hormone which causes growth of the yellow body of the ovary and also stimulates activity of the interstitial cells of the testis.
LuxThe unit of illuminance equivalent to 1lumen per square meter.
luxury consumptionNutrient absorption by an organism in excess of that required for optimum growth and productivity.
lyaseAny of a class of enzymes that catalyse either the cleavage of a double bond and the addition of new groups to a substrate, or the formation of a double…
Lymph NodeA small rounded or bean-shaped mass of lymphatic tissue that helps the body's immune system.
Lymph nodes(LIMF nohdz): Small glands that help the body fight infection and disease. They filter a fluid called lymph and contain white blood cells.
Lymphatic system(lim-FA-tik SIS-tem) The tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases.
Lymphocyte(LIM-foh-site) A type of white blood cell. Lymphocytes have a number of roles in the immune system, including the production of antibodies and other…
Lymphoid(LIM-foyd) Referring to lymphocytes, a type of white blood cell. Also refers to tissue in which lymphocytes develop.
lymphokineGeneric name for proteins that are released by lymphocyte s to act on other cells involved in the immune response.
lymphoma(lim-FOH-muh) Cancer that begins in cells of the immune system. There are two basic categories of lymphomas.
LysimeterAn isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil.
lysis(LY-sis) In biology, lysis refers to the breakdown of a cell caused by damage to its plasma (outer) membrane.
lysogenyA condition in which a bacteriophage genome (pro-phage ) survives within a host bacterium, either as part of the host chromosome or as part of an…
lysosomeA sac-like compartment inside a cell that has enzymes that can break down cellular components that need to be destroyed.
lysozymeA naturally occurring enzyme extracted from egg white protein and other animal and plant sources, which attacks the cell wall of gram-positive bacteria…
lyticHaving to do with lysis. In biology, lysis refers to the disintegration of a cell by disruption of its plasma membrane.
lytic cycleThe steps in viral production that lead to cell lysis.
M 3000In solar-terrestrial terms, the optimum high frequency radio wave with a 3000 km range, which reflects only once from the ionosphere (single hop…
M13A single-stranded DNA bacteriophage used as a vector for DNA sequencing.
M13 strandThe single-stranded DNA molecule that is present in the infective form of bacteriophage M13.
M2/S2m2/s2 (meters squared per second squared), unit of measure equivalent to J/kg (joules per kilogram).
MAAPAbbreviation for multiple arbitrary amplicon profiling.
MaarA volcanic crater that is produced by an explosion in an area of low relief, is generally more or less circular, and often contains a lake, pond, or marsh.
macerateTo disintegrate tissue to disrupt cells. Commonly achieved via mechanical shearing, plasmolysis or enzymatic cell wall degradation.
Mackeral SkyThe name given to cirrocumulus clouds with small vertical extent and composed of ice crystals. The rippled effect gives the appearance of fish scales.
MacroburstA convective downdraft with an affected outflow area of at least 2½ miles wide and peak winds lasting between 5 and 20 minutes.
MacroclimateThe climate representative of relatively large area.
MacrohabitatAn extensive habitat presenting considerable variation of the environment, containing a variety of ecological niches and supporting a large number and…
macromoleculeAny high molecular weight molecule. Often used as a synonym for polymers.
macronutrientA major chemical element essential for normal growth and development. In tissue culture media, macronutrients are those required in concentrations above 0.
macrophageA type of white blood cell that surrounds and kills microorganisms, removes dead cells, and stimulates the action of other immune system cells.
Macrophyte (aquatic)An aquatic plant that is large enough to be observed with the naked eye. It grows in or near water.
MacrophytesA plant large enough to be seen by the naked eye.
mad cow diseaseColloquial term for bovine spongiform encephalopathy. See proteinaceous infectious particle
Madden-Julian Oscillation(abbrev. MJO)- Tropical rainfall exhibits strong variability on time scales shorter than the seasonal El Niño-Southern Oscillation (ENSO).
MADS boxA highly conserved DNA sequence motif found in a large family of transcription factors, most of which play important roles in developmental processes.
Mafic (or maphic)A term used to describe an igneous rock that has a large percentage of dark-colored minerals such as amphibole, pyroxene, and olivine.
MAFOR(Great Lakes Marine Forecast) - A National Weather Service coded summary appended to each of the Great Lakes Open Lakes forecasts.
MagentaUsed in four color printing. Reflects blue & red and absorbs green.
MagflareIn solar-terrestrial terms, a geomagnetic and/or cosmic storm has been associated with this flare
MagmaMolten or partially molten rock at temperatures ranging from 1,260 F to 2,880 F (700 C to 1600 C).
Magnetic BallastA type of florescent light ballast that uses a magnetic core to regulate the voltage of a florescent lamp.
Magnetic BayIn solar-terrestrial terms, a relatively smooth excursion of the H (horizontal) component of the geomagnetic field away from and returning to quiet levels.
Magnetic FieldA field of force around the Sun and the planets, generated by electrical currents, in which a magnetic influence is felt by other currents.
Magnetic Field LinesA magnetic field has both a strength and a direction at each point in space. For example, at each point Earth, the magnetic field -- and thus a compass --…
Magnetic LoopsField lines illuminated by hot plasma flowing along the magnetic field lines.
Magnetic poleMagnetic Pole Either of the two points on the Earth's surface at which magnetic meridians converge.
Magnetic Storms and SubstormsA series of terrestrial disturbances – namely, the precipitation of auroras and rapid changes in Earth's magnetic field – caused by high-speed blasts…
MagnetismA force generated by electrical currents and changing electric fields. Magnetism is responsible for almost every feature in the solar atmosphere, from…
MagnetogramA magnetogram is an image of the Sun's magnetic flux. They are derived by using emission lines which are magnetically sensitive, which allows the magnetic…
MagnetopauseIn solar-terrestrial terms, the boundary layer between the solar wind and the magnetosphere.
MagnetosphereAn area around a planet in which the planet’s magnetic field is stronger than the magnetic field carried by the solar wind.
MagnetotailThe long magnetic tail of a magnetosphere drawn out by the flow of the solar wind.
MagnitudeA rating of a given earthquake, independent of the place of observation. It is calculated from measurements on seismographs and it is expressed in…
MainThe principal pipe artery to which branches may be connected.
Main channelThe deepest or central part of the bed of a stream, containing the main current.
Main channel poolReach of a stream or river with a low bed elevation, relative to rapids or riffles.
Main Sequence StarA star that lies along a continuous band, known as the main sequence, extending from the upper left (hot, bright stars) to the lower right (cool, dim…
Main StemThe reach of a river/stream formed by the tributaries that flow into it.
Main Synoptic TimesThe times of 0000, 0600, 1200, and 1800 UTC. Also known as the standard synoptic times.
Mainstream (mainstem)The main course of a stream where the current is the strongest.
maintenanceThe patent fees due at 4, 8 and 12 years needed to keep a U. S. utility or plant patent in force for its full life.
Maintenance areaAny geographic region of the United States previously designated nonattainment pursuant to the CAA Amendments of 1990 and subsequently redesignated to…
Maintenance management systemAny organized system used to ensure that all operations and maintenance activities (e.g.
Major facilityA term used by Reclamation to describe those facilities for which an examination is conducted every third year, alternately conducted by the Denver and…
Major FlareIn solar-terrestrial terms, this flare is the basis for the forecast of geomagstorm, cosmic storm and/or protons in the earth's vicinity
Major FloodingA general term including extensive inundation and property damage. (Usually characterized by the evacuation of people and livestock and the closure of…
major histocompatibility antigenA cell-surface protein or glycoprotein that allows the immune system to distinguish foreign or "non-self" from "self". A better term is histoglobulin.
major histocompatibility complex(Abbreviation: MHC). The large cluster of genes that encode the major histocompatibility antigens in mammals.
Major histocompatibility complex (MHC)A group of genes that code for cell-surface histocompatibility antigens. These antigens are the primary reason why organ and tissue transplants from…
Major HurricaneA hurricane which reaches Category 3 (sustained winds greater than 110 mph) on the Saffir/Simpson Hurricane Scale.
Major sourceA source that emits, or has the potential to emit, a pollutant regulated under the Clean Air Act in excess of a specified rate in a nonattainment area.