A pure function is a function that, given the same input, will always return the same output and has no side effects. This means that it doesn't modify variables outside its scope, interact with external systems (such as databases or APIs), or produce any observable effects other than computing its return value. Pure functions are deterministic, meaning they rely only on their input parameters and don't depend on any external state. Characteristics of pure functions: Deterministic: Given the same inputs, a pure function will always produce the same output, making its behavior predictable. No Side Effects: Pure functions don't modify variables outside their scope or affect the state of the program in any observable way. They only depend on their input parameters. Referential Transparency: This property means that you can replace a function call with its result without changing the behavior of the program. This is possible because pure functions always produce the same output for the same input.