Functional programming is programming paradigm that talks about programming with functions that takes arguments and returns a value . But the real question here is what is different in functional programming than the other paradigms?
Functional programming has no observable result other than returning a value. A function can have no effect other than producing its result. In traditional imperative style programming it's a series of mutation, separated with conditions. The emphasis is more on how the things needs to be done. Functional Programming is about what needs to be done.