If you know PHP, you know that it's written in C. If you know C, you also know that it's statically typed. What does this mean? This means that you need to declare the type of a variable when you are declaring the variable. This is how you declare a variable in C: int a = 0; And this is how you do the same in PHP: $a = 0; So how does PHP know that $a is an integer and not a string? Or any other type? How does PHP convert this dynamic typing into static typing for the underlying C code? To understand this, you need to understand how PHP handles variables in it's code. And that's what we are going to