undefined in JavaScript

js-undefined.js

var emp = {
    name: 'John Snow',
    email: 'john.snow@abc.com'
}

console.log(emp.name);
//John Snow
console.log(emp.address);
// undefined (here we are trying to extract a member which object doesn't have)

var test;
console.log(test);
//undefined (a variable defined but not initialized)