beta reduction

Noun

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x.\; t)$ to a term $s$ yields an expression $t[s/x]$, "t with s instead of x", where all free instances of x in t have been replaced by s.