undefined Not defined
1. A variable was declared with a keyword "var" but not assigned with a value. A variable have not been declared without assignment:
2. Example :
var a = 1, b;
console.log(a) //1
console.log(b) //undefined 		Example :
var a = 1, b;
console.log(f) // not defined
BY Best Interview Question ON 08 Sep 2022