A reduction in generality, usually for the sake of increased efficiency. If a piece of code is specialised for certain values of certain variables (usually function arguments), this is known as "partial evaluation". In a language with overloading (e.g. Haskell), an overloaded function might be specialised to a non-overloaded instance at compile-time if the types of its arguments are known.
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Nearby terms: SPECIAL « special-case « Special Interest Group « specialisation » specification » specific markup » SPECint92