This glossary defines lubrication and tribology terms used in standards based documentation, OEM specifications, and lubricant technical literature. Definitions are written for reference and do not replace equipment documentation.
Terms are grouped by topic and can be expanded over time as new equipment categories are added to the Technical Hub.
Lubrication regimes and contact conditions
Boundary lubrication
A regime where surface contact occurs and additives play a significant role in wear control.
Mixed lubrication
A regime where part of the load is supported by a fluid film and part by surface contact.
Hydrodynamic lubrication
A regime where a full fluid film separates surfaces under relative motion.
Elastohydrodynamic lubrication
A regime common in rolling element contacts where elastic deformation and viscosity increase support film formation.
Wear and surface terms
Abrasion
Wear caused by hard particles or asperities cutting or ploughing a surface.
Adhesive wear
Wear caused by material transfer between surfaces in contact under load.
Scuffing
Surface damage associated with severe sliding contact and local welding effects.
Pitting
Surface fatigue resulting in small pits, often associated with rolling contact fatigue.
Micropitting
Fine surface fatigue damage often appearing as grey staining under specific contact conditions.
Oil condition and stability
Oxidation stability
Resistance to oxidation under defined test conditions.
Nitration
Chemical process in engine oils associated with combustion by products and nitrogen oxides.
Viscosity change
Change in measured viscosity from new oil values, reported at defined temperatures.
Acidity
A property often reported as total acid number in oil condition reporting contexts.
Base reserve
A property often reported as total base number in engine oil contexts.
Water, air, and contamination control
Demulsibility
Ability of an oil to separate from water under defined conditions.
Foaming
Presence and persistence of air bubbles in a lubricant under defined conditions.
Air release
Tendency of entrained air to separate from a lubricant.
Filterability
How readily a lubricant passes through filtration media under defined conditions.