Definition - What does Functional Programming mean?
Functional programming is a software development model. It estimates and applies mathematical functions, rather than state or mutable data and imperative code threads. The real origins of functional programming are lambda calculus and formal system sciences, which apply function definition, application and recursion.
Techopedia explains Functional Programming
Functional programming makes language code threads result in the same values, regardless of the time or machine running the code thread. This is not the case with imperative function programming, which often has unpredictable program responses.
Many (most?) commercial software developers, often inexperienced with mathematical models, apply imperative function programming rather than functional programming. This results in crash-vulnerable commercial programs with unacceptable responses.
Functional programming can be realized in any language, even one not designed with default functional programming structures.