From "Abrasion" to "ZDDP" our comprehensive glossary helps you understand the technical terms specific to lubricants, coolants, and more.

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  • absolute viscosity

    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 (see viscosity). Absolute viscosity divided by the fluid’s density equals kinematic viscosity.

  • absorption

    the taking up, assimilation, or incorporation of one material into another.

  • acid

    a chemical substance that can react with metals to form salts and with bases or alkalies to form salts plus water. Acids contain hydrogen and they form hydrogen ions (H+) in water. They are considered strong or weak depending on the hydrogen ion concentration in the solution.

  • acid number

    see neutralization number.

  • additive

    a chemical added in small quantities to a petroleum product to impart or improve certain properties.

  • AGMA

    American Gear Manufacturers Association, which as one of its activities establishes and promotes standards for gears and lubricants.

  • alkaline

    the property of a substance, product, or mixture that gives it the chemical character of a base or alkali, as contrasted to an acid.

  • aniline point

    lowest temperature at which a specified quantity of aniline (a benzene derivative) is soluble in a specified quantity of a petroleum product, as determined by test method ASTM D 611 or D 1012; hence, an empirical measure of the solvent power of a hydrocarbon.

  • antifoam agent

    one of two types of additives used to reduce foaming in petroleum products: silicone oil to break up large surface bubbles; and various kind of polymers that decrease the amount of small bubbles entrained in the oils.

  • antioxidant

    see oxidation inhibitor.

  • antiwear agent

    an additive that minimizes wear caused by metal-to-metal contact during conditions of mild boundary lubrication (e.g., stops and starts, oscillating motion). The additive reacts chemically with, and forms a film on metal surfaces under normal operating conditions.

  • API (American Petroleum Institute)

    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 gravity

    see specific gravity.

  • API Service Categories

    gasoline and diesel engine oil quality levels established jointly by API, SAE, and ASTM, and sometimes called SAE or API/SAE categories.

  • aromatic

    unsaturated hydrocarbon identified by one or more benzene rings or by chemical behavior similar to benzene.

  • ash content

    noncombustible residue of a lubricating oil or fuel, determined in accordance with ASTM D 582 and D 874 (sulfated ash).

  • ashless dispersant

    cleanliness additive for crankcase oils. It is widely used in lubricants for aviation piston engines. Unlike conventional crankcase-oil detergents, ashless dispersants do not contain metallic compounds. See dispersant.

  • ASLE (American Society of Lubrication Engineers)

    an organization intended to advance the knowledge and application of lubrication and related sciences.

  • ASTM (American Society for Testing and Materials)

    an organization devoted to “the promotion of knowledge of the materials of engineering, and the standardization of specifications and methods of testing.” A preponderance of the data used to describe, identify, or specify petroleum products is determined in accordance with ASTM test methods.

  • autoignition temperature

    minimum temperature at which a combustible fluid will burst into flame without an extraneous ignition source.