Dictionary.net

The application of a lambdaabstraction to an argument expression. A copy of the body ofthe lambda abstraction is made and occurrences of the boundvariable being replaced by the argument. E.g. (\ x . x+1) 4 --> 4+1Beta reduction is the only kind of reduction in the purelambda-calculus. The opposite of beta reduction is betaabstraction. These are the two kinds of beta conversion.See also name capture.