Variable Environments:

Where the variable live and how they relate to each other in memory.

function b (){
    var myVar;
}

function a () {
    var myVar = 2;
    b();
}

var myVar = 1;
a();

What is the value of myVar? 
    - Globar Execution Context is executed (myVar = 1)
    - a() -> New Execution Context is created for a() - 
         Every execution context has its own execution context so myVar = 2
    - b() -> New Execution Context with its own variable environment and memory space so myVar = Undefined 
 This Has something to do with scope. 
 This means where are able to see the variable. Each variable is defined in its own 'execution context' 
 as it is within a function. 
 Every time you call a function, you get a new execution context. 

 Even though the myVar is declared 3 times, they are uniqued

Summary: