A.G.M.A.	: Abbreviation for "American Gear Manufacturers Associations," an organization serving the gear industry.
A.S.T.M.	: American Society for Testing Materials" a society for developing standards for materials and test methods.
Abrasion	: a general wearing away of a surface by constant scratching, usually due to the presence of foreign matter such as dirt, grit, or metallic particles in the lubricant. It may also cause a break down of the material (such as the tooth surfaces of gears). Lack of proper lubrication may result in abrasion.
Abrasive wear (or cutting wear)	: comes about when hard surface asperities or hard particles that have embedded themselves into a soft surface and plough grooves into the opposing harder surface, e.g., a journal.
Absolute filtration	: rating the diameter of the largest hard spherical particle that will pass through a filter under specified test conditions. This is an indication of the largest opening in the filter elements.
Absolute Pressure	: The sum of atmospheric and gage pressure.
Absolute Viscosity	: a term used interchangeably with viscosity to distinguish it from either kinematic viscosity or commercial viscosity. Absolute viscosity is the ratio of shear stress to shear rate. It is a fluid's internal resistance to flow. The common unit of absolute viscosity is the poise. Absolute viscosity divided by fluid density equals kinematic viscosity. It is occasionally referred to as dynamic viscosity. Absolute viscosity and kinematic viscosity are expressed in fundamental units. Commercial viscosity such as Saybolt viscosity is expressed in arbitrary units of time, usually seconds.
Absorbent filter	: a filter medium that holds contaminant by mechanical means.
Absorption	: the assimilation of one material into another; in petroleum refining, the use of an absorptive liquid to selectively remove components from a process stream.
AC Fine Test Dust (ACFTD)	: A test contaminant used to assess both filters and the contaminant sensitivity of all types of tribological mechanisms.
Accumulator	: a container in which fluid is stored under pressure as a source of fluid power.
Acid	: in a restricted sense, any substance containing hydrogen in combination with a nonmetal or nonmetallic radical and capable of producing hydrogen ions in solution.
Acid number	: The quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.
Acid sludge	: The residue left after treating petroleum oil with sulfuric acid for the removal of impurities. It is a black, viscous substance containing the spent acid and impurities.
Acid treating	: A refining process in which unfinished petroleum products, such as gasoline, kerosene, and lubricating oil stocks, are contacted with sulfuric acid to improve their color, odor, and other properties
Acidity in lubricants,	: acidity denotes the presence of acid-type constituents whose concentration is usually defined in terms of total acid number. The constituents vary in nature and may or may not markedly influence the behavior of the lubricant.
Actuator	: A device used to convert fluid energy into mechanical motion.
Additive	: A chemical substance added to a petroleum product to impart or improve certain properties. Common petroleum product additives are: antifoam agent, anti-wear additive, corrosion inhibitor, demulsifier, detergent, dispersant, emulsifier, EP additive, oiliness agent, oxidation inhibitor, pour point depressant, rust inhibitor, tackiness agent, viscosity index (VI.) improver.
Additive level	: The total percentage of all additives in an oil. (Expressed in % of mass (weight) or % of volume)
Additive stability	: the ability of additives in the fluid to resist changes in their performance during storage or use.
Adhesion	: the property of a lubricant that causes it to cling or adhere to a solid surface.
Adhesive wear	: is often referred to as galling, scuffing, scoring, or seizing. It happens when sliding surfaces contact one another, causing fragments to be pulled from one surface and to adhere to the other.
Adsorbent	: filter a filter medium primarily intended to hold soluble and insoluble contaminants on its surface by molecular adhesion.
Adsorption	: adhesion of the molecules of gases, liquids, or dissolved substances to a solid surface, resulting in relatively high concentration of the molecules at the place of contact; e.g. the plating out of an anti-wear additive on metal surfaces.
Adsorptive filtration	: the attraction to, and retention of particles in, a filter medium by electrostatic forces, or by molecular attraction between the particles and the medium.
Aeration the state of air being suspended in a liquid such as a lubricant or hydraulic fluid.
Agglomeration	: the potential of the system for particle attraction and adhesion.
AGMA lubricant numbers	: AGMA specification covering gear lubricants. The viscosity ranges of the AGMA numbers (or grades) conform to the International Standards Organization (ISO) viscosity classification system (see ISO viscosity classification system).
Air Bleeder	: A device for removal of air from a hydraulic fluid line.
Air Breather	: a device permitting air movement between atmosphere and the component in/on which it is installed.
Air entrainment	: The incorporation of air in the form of bubbles as a dispersed phase in the bulk liquid. Air may be entrained in a liquid through mechanical means and/or by release of dissolved air due to a sudden change in environment. The presence of entrained air is usually readily apparent from the appearance of the liquid (i.e., bubbly, opaque, etc.) while dissolved air can only be determined by analysts.
Air motor	: A device which converts compressed gas into mechanical force and motion. It usually provides rotary mechanical motion.
Air, Compressed air	: at any pressure greater than atmospheric pressure.
Air, free Air	: at ambient temperature, pressure, relative humidity, and density.
Air/Oil Systems	: A lubrication system in which small measured quantities of oil are introduced into an air/oil mixing device which is connected to a lube line that terminates at a bearing, or other lubrication point. The air velocity transports the oil along the interior walls of the lube line to the point of application. These systems provide positive air pressure within the bearing housing to prevent the ingress of contaminants, provide cooling air flow to the bearing, and perform the lubrication function with a continuous flow of minute amounts of oil.
Air-Gap solenoid	: A solenoid that is sealed to prevent leakage of the liquid indo the plunger cavity
Alkali	: any substance having basic (as opposed to acidic) properties. In a restricted sense it is applied to the hydroxides of ammonium, lithium, potassium and sodium. Alkaline materials in lubricating oils neutralize acids to prevent acidic and corrosive wear in internal combustion engines.
Almen EP lubricant tester	: A journal bearing machine used for determining the load-carrying capacity or Extreme Pressure properties (EP) of gear lubricants.
Aluminum alloy	: White particles which indicate wear of aluminum component such as a casing wall.
Ambient temperature	: Temperature of the area or atmosphere around a process, (not the operating temperature of the process itself).
amp	: ampere
Analytical ferrography	: the magnetic precipitation and subsequent analysis of wear debris from a fluid sample This approach involves passing a volume of fluid over a chemically treated microscope slide which is supported over a magnetic field. Permanent magnets are arranged in such a way as to create a varying field strength over the length of the substrate. This varying strength causes wear debris to precipitate in a distribution with respect to size and mass over the Ferrogram. Once rinsed and fixed to the substrate, this debris deposit serves as an excellent media for optical analysis of the composite wear particulates.
Anhydrous	: devoid of water.
Aniline	: point The minimum temperature for complete miscibility of equal volumes of aniline and the sample under test ASTM Method D611. A product of high aniline point will be low in aromatics and naphthenes and, therefore, high in paraffins. Aniline point is often specified for spray oils, cleaning solvents, and thinners, where effectiveness depends upon aromatic content. In conjunction with API gravity, the aniline point may be used to calculate the net heat of combustion for aviation fuels.
ANSI	: American National Standards Institute
Anti-foam agent	: one of two types of additives used to reduce foaming in petroleum products: silicone oil to break up large surface bubbles, and various kinds of polymers that decrease the amount of small bubbles entrained in the oils.
Anti-friction	: bearing a rolling contact type bearing in which the rotating or moving member is supported or guided by means of ball or roller elements. Does not mean without friction.
Anti-oxidants	: prolong the induction period of a base oil in the presence of oxidizing conditions and catalyst metals at elevated temperatures. The additive is consumed and degradation products increase not only with increasing and sustained temperature, but also with increases in mechanical agitation or turbulence and contamination
Antistatic	: additive an additive that increases the conductivity of a hydrocarbon fuel to hasten the dissipation of electrostatic charges during high-speed dispensing, thereby reducing the fire/explosion hazard.
Antiwear	additives improve the service life of tribological elements operating in the boundary lubrication regime. Antiwear compounds (for example, ZDDP and TCP) start decomposing at 90 degrees to 100 degrees C and even at a lower temperature if water (25 to 50 ppm) is present.
API	(American Petroleum Institute) A trade association of petroleum producers, refiners, marketers, and transporters, organized for the advancement of the petroleum industry by conducting research, gathering and disseminating information, and maintaining cooperation between government and the industry on all matters of mutual interest.
API engine service categories	: gasoline and diesel engine oil quality levels established jointly by API, SAE, and ASTM, and sometimes called SAE or API/SAE categories; formerly called API Engine Service Classifications.