This glossary defines commonly used lubricant and tribology terms referenced in technical documentation, specifications, standards frameworks, and product data sheets. Definitions are descriptive and provided to support consistent interpretation of technical language used in industrial and automotive lubrication.
Terms are presented as reference definitions only. Interpretation of requirements, performance suitability, and application limits should always be confirmed against relevant standards and original equipment manufacturer documentation.
Core terminology
Viscosity
A measure of a fluid’s resistance to flow at a specified temperature, influencing film thickness, load carrying capability, and flow behaviour.
Kinematic viscosity
Viscosity measured under gravity flow conditions, typically expressed in square millimetres per second (mm²/s) at a defined temperature.
Viscosity index
A dimensionless indicator describing the rate at which a lubricant’s viscosity changes with temperature.
Base oil
The primary fluid component of a lubricant formulation, providing the fundamental lubrication properties before the addition of performance additives.
Additive
A chemical component incorporated into a lubricant to modify or enhance specific performance characteristics such as wear protection, oxidation resistance, or cleanliness.
Shear stability
The ability of a lubricant to maintain its viscosity characteristics when subjected to mechanical stress in service.
Oxidation
A chemical reaction between lubricant components and oxygen, typically accelerated by elevated temperature and contaminants, which can lead to degradation over time.
Foaming
The formation and persistence of air bubbles within a lubricant, which can impair lubrication effectiveness and system performance.
Air release
The ability of entrained air to separate from a lubricant under static conditions.
Demulsibility
The ability of a lubricant to separate from water, supporting corrosion protection and consistent lubrication performance.
Wear protection
A general term describing lubricant properties that reduce surface damage and material loss under load and boundary lubrication conditions.