Author's Homepage:   Kurt M. Marshek
Chapter 13: Lubrication and Sliding Bearings
"The word bearing, applied to a machine or structure, refers to contacting surfaces through which a load is transmitted. When relative motion occurs between the surfaces, it is usually desirable to minimize friction and wear. Any interposed substance that reduces friction and wear is a lubricant. Lubricants are usually liquid but can be a solid, such as graphite, TRE, or molybdenum disulfide, or a gas, such as pressurized air."