File Upload Multiple via aJax - PHP

The problem is that you create FormData to send but not add any of the files in it and your POST ends up empty.

Here's how you can do it:

var $jq = jQuery.noConflict();
$jq(function(){

    var bsUpload = $jq("#bsUpload");

    bsUpload.on('click', 'input[name="btEnviar"]', function(event){
        event.preventDefault();

        var formdata = new FormData();

        $jq.when($jq('.fileUpload').each(function(i,e) {
            // adiciona uma entrada em "formdata" para cada campos de classe "fileUpload" com arquivo selecionado
            var file = e.files[0];
            if(file)
                formdata.append('fileUpload['+i+']', file);
        })).done(function(){
            $jq.ajax({
                type: 'POST', cache: false, processData: false, contentType: false, 
                url: 'upload.php', data: formdata,
                success: function(j){
                   alert(j);
                }
            });
        });
    });
});

And as @Daniela mentioned, to avoid this kind of error in PHP you should always check if the index actually exists in the array.

Your PHP would look like this:

if (isset($_FILES['fileUpload'])) {
    foreach($_FILES['fileUpload']['error'] as $key => $error){
        if($error == UPLOAD_ERR_OK){
            $name = $_FILES['fileUpload']['name'][$key];
            move_uploaded_file($_FILES['fileUpload']['tmp_name'][$key], '../../upload/'.$name);
        }
    }

    echo 'Envio ok';

} else {
    echo 'Nenhum arquivo enviado';
}

You should add a few more checks in your PHP code to make sure the files were actually uploaded and no errors occurred in the process.

The first alert is why you did not check if fileUpload was an index of $_FILES .

<?php    
if (isset($_FILES['fileUpload'])) {

}

The second error occurred because you are trying to iterate $_FILES['fileUpload']['error'] which is not an array, in which case you should use switch .

<?php    
if (isset($_FILES['fileUpload'])) {
    switch ($_FILES['fileUpload']["error"]) {
        case UPLOAD_ERR_OK:        
            break;
    }
}