Answer

A Higher-Order Function is a function that:

1. Takes another function as a parameter.
2. OR returns a function.

Example

```kotlin // Takes a function 'operation' fun calculate(a: Int, b: Int, operation: (Int, Int) -> Int): Int { return operation(a, b) }

// Usage val sum = calculate(5, 10) { x, y -> x + y } val mul = calculate(5, 10) { x, y -> x * y } ```

This is the foundation of Kotlin's functional programming features like `map`, `filter`, and callbacks.