Lambda calculus

Lambda calculus is a mathematical syntax for expressing computations. The fundamental lambda term is defined, where $M,N$ are lambda terms:

• $x,y,\dots$ — are variables that represent a parameter. We assume to have infinitely many.
• $(\lambda x.M)$ — is the abstraction (or expression) of $M$ over the variable $x$.
• $(MN)$ — is the combination (or application) of $M$ and $N$.

Lambda calculus is broadly used in functional programming (but like many FP concepts, it has spread) via the use of lambda functions.

https://lawrencecpaulson.github.io/2024/09/30/Intro_Lambda_Calculus.html