Explain the concept of an empty interface and in which cases it is used.

In Go, an empty interface (interface{}) is an interface that contains no methods. It can represent a value of any type because all types implement the empty interface by default.

This allows interface{} to be used as a universal container for storing values of different types.

Example usage:

func printValue(v interface{}) {
    fmt.Println(v)
}

printValue(42)       // int
printValue("hello") // string
printValue(3.14)     // float64

An empty interface is often used when working with data of unknown type, such as when handling JSON, or for creating generic functions and structures.