ELI5: Explain Like I'm 5

lambda calculus

Lambda calculus is like a game where you can make up rules that help you solve math problems. The game works like this: when you start off, you have some kinds of pieces called lambda terms. You can move the pieces around and combine them in different ways that follow the rules of the game. Then, when you're done, you look at the pieces and you can figure out the answer to the math problem.