Functional Programming is a declarative programming paradigm that treats computation as the evaluation of mathematical functions, emphasizing immutability, pure functions, and avoiding side effects. Unlike imperative programming which focuses on how to execute step-by-step instructions, functional programming focuses on what to compute by composing functions. At its core lies the principle that data flows through transformations rather than being mutated in place, enabling powerful abstractions like higher-order functions, lazy evaluation, and referential transparency that make code more predictable, testable, and easier to reason about—especially in concurrent and parallel environments.