Lambda abstraction
A lambda abstraction is an abstract lambda expression[?]. It is expressed in the language of lambda calculus. A lambda abstraction is to a functional programming language such as Scheme what pseudo-code[?] is to an imperative programming language.
More specifically, a lambda abstraction is a lambda expression with no free variables: each its variables is bound by some lambda. E.g.
is a concrete lambda expression, whereas
is an abstract lambda expression.