so => means 'is assigned to'
You could say that's part of it. When creating an array you can use => to specify the index that a value should have.
It's also used in foreach loops when you want to loop over an array and need to know both the current index of the array and the value stored at that index. It's especially useful when working with associative arrays.
A modified example from the manual:
$a = array(
"one" => 1,
"two" => 2,
"three" => 3,
"seventeen" => 17
);
foreach ($a as $i => $value) {
echo "Index '$i' has value $value.\n";
}
/*
Output:
Index 'one' has value 1.
Index 'two' has value 2.
Index 'three' has value 3.
Index 'seventeen' has value 17.
*/
