algebra

The term algebra is used ... to denote abstract behaviour of a class of objects ...
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While a calculus is a general-purpose syntactic system of transformation rules, an algebra is a special-purpose semantic system that captures specific behaviour such as that of the integers or of stacks, persons or vehicles. A given algebra can generally be captured by a variety of syntactic calculi. For example, the behaviour of integers can be realised by decimal or binary number systems or even by lambda calculus representations. An algebra may be thought of as an equivalence class of calculi with common behaviour or as an abstraction from a specific syntactic realisation of a calculus to a semantic specification of the underlying behaviour.

-- Wegner. The Object-Oriented Classification Paradigm. 1987