What is a lambda (function)?

Question

For a person without a comp-sci background, what is a lambda in the world of Computer Science?

Answer 1

It refers to lambda calculus, which is a formal system that just has lambda expressions, which represent a function that takes a function for its sole argument and returns a function. All functions in the lambda calculus are of that type, i.e., λ : λ → λ.

Lisp used the lambda concept to name its anonymous function literals. This lambda represents a function that takes two arguments, x and y, and returns their product:

(lambda (x y) (* x y)) 

It can be applied in-line like this (evaluates to 50):

((lambda (x y) (* x y)) 5 10)