PHP is loosely typed, meaning that it will implicitly change the type of a variable as needed,
depending on the operation being performed on its value.
This contrasts with strongly typed languages, like C and Java,
where variables can only contain one type of data throughout their existence.
Variables must be named using only letters, numbers and underscore. Must start with a letter or an underscore.
$name = 'valid'; // Valid name
$_name = 'valid'; // Valid name
$1name = 'invalid'; // Invalid name, starts with a number
Are one of only two identifier types in PHP that are case-sensitive (the other is constants)
$Name = "John";
echo $name; // Notice: Undefined variable: name