Thank you for the clarification, but it was not clear what you where asking in the initial post.
The initial post was very vague and did not include the details that you where asking about the "$_FILES["up"]" versus "$_FILES["image"]" code.
The $_FILES collection is much like the $_FORM or $_GET collection, but for File fields in a multipart/form-data encoded form.
There is a $_FILE variable for each File field you add to the form, in the same way that each text element in the form will have a $_POST variable.