A concise, universal formalism suitable for reasoning about
mathematical functions. All expressions are anonymous functions, that is, instead of writing
f(x) = x+2 for every x
you just write
f = λ(x).(x+2)
So lambda calculus denotes functions without naming them.
(λ(x).(x+2) is lambda calculus, the f = isn't.)
An interesting aspect is that + and even 2 can
themselves be defined in terms of lambda calculus:
it is a complete description of discrete computation.