So then what are those numbers and funny arrows (=>)? Well, PHP arrays are
associative arrays. That’s why you can say, for example, $_REQUEST[‘user_pic’].
The $_REQUEST array doesn’t just have values, but it actually has an association
between those values (the information in an HTML form, usually) and the name
of the fields in which those values appeared.
You can think of the mapping between the field name user_pic and the value of
that field—something like profile_pic.jpg, for example—as being defined like this: