In thermodynamics, property, particularly as defined in engineering thermodynamics, is a term, commonly defined as any quantity which serves to describe a system, used synonymously or rather in place of “variable”, e.g. intensive property (vs. intensive variable) or extensive property (vs. extensive variable) the latter, i.e. variable, being the more common usage in general thermodynamics. [1]

References
1. Potter, Merle C. and Somerton, Craig W. (2009). Schaum's Outlines: Thermodynamics for Engineers (pg. 3). McGraw-Hill.

Further reading
‚óŹ Moran, Michael J., Shapiro, Howard N., Boettner, Daisie D., and Bailey, Margaret. (2010). Fundamentals of Engineering Thermodynamics (§1.3.2: Property, State, and Process; §1.3.3: Extensive and Intensive Properties, pgs. 9-). John Wiley and Sons.

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