beta reduction

noun2

1. •
   The act of beta reducing, an instance of replacing a function call by the result of calling a function.
2. •
   One of the three rewrite rules of the lambda calculus, which states that the application of a lambda abstraction (λx.t) to a term s yields an expression t[s/x], "t with s instead of x", where all free instances of x in t have been replaced by s.