下列文字摘自What is This “Lambda” You Speak Of?：
lambda means “anonymous function,” and calculus means “a formal system”
Therefore, the term lambda calculus refers to “a formal way to think about functions.”
That same Wikipedia link states this:
“Lambda calculus provides a theoretical framework for describing functions and their evaluation. Although it is a mathematical abstraction rather than a programming language, it forms the basis of almost all functional programming languages today.”
When I first started learning about functional programming, I found these terms to be a little intimidating, but as with most FP terms, they’re just uncommon words for talking about “functions and their evaluation.”