What does the "..." (triple dot) notation in arrays mean?

I don't understand what the ... notation does exactly.

I tried a simple example with Babel to understand it (view the example), but it seems that:

ES6 syntax

let myArray = [1, 2, 3, ...18];

console.log(myArray); // [1, 2, 3]
console.log(myArray[4]);// undefined
console.log(myArray.length); // 3

is the same as this ES5 syntax:

"use strict";

function _toConsumableArray(arr) { 
    if (Array.isArray(arr)) { 
        for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) {
             arr2[i] = arr[i];
        }
        return arr2;
     } else { 
        return Array.from(arr); 
     } 
}

var myArray = [1, 2, 3].concat(_toConsumableArray(18));

console.log(myArray); // [1, 2, 3]
console.log(myArray[4]); // undefined
console.log(myArray.length); // 3

BUT: What does this code do? Because the output (console.log) is the same as in this code (ES5):

var myArray = [1,2,3];

console.log(myArray); // [1, 2, 3]
console.log(myArray[4]);// undefined
console.log(myArray.length); // 3

What does the ...18 notation mean?