<script>
    $(document).ready(function() {
        $('body').on('click', '.save', function(e) {
            var string = $(this).serialize();
            $.ajax({
                type: "POST",
                url: "add_room.php",
                data: string,
                cache: false,
                success: function(data){
                    $('#message').text('The id of the inserted information is ' + data);
                }
            });
        });
    });
    $(document).ready(function(){
        $('#addForm').on('click', function(){
            $('<label for="itemName[]">Item</label><input class="itemName" type="text" name="itemName[]"><label for="itemCondition">Condition</label><input class="itemCondition" type="text" name="itemCondition"><div class="save">Save Item</div>').fadeIn(500).appendTo('#mainForm');
        });
    });
    </script>

<?PHP

    include('dbConfig.php');

    $item = $db->real_escape_string($_POST['itemName']);

    if ($stmt = $db->prepare("INSERT test (test_title) VALUES (?)"))
    {
        // Use an s per variable passed to the string, example - "ss", $firstname, $lastname
        $stmt->bind_param("s", $item);
        $stmt->execute();
        $stmt->close();

        echo $db->insert_id;
        //echo "success";
    }
    // show an error if the query has an error
    else
    {
        echo "ERROR: Could not prepare SQL statement.";
    }
?>

var string = $(this).closest('form').serialize();

var string = $('#input1,#nextone,#somefield').serialize();

var string = $(this).serialize();

$_POST['itemName']

<form method="POST" class="save" action="add_room.php">
<input type="text" name="itemName[]"/>
<input type="text" name="itemName[]"/>
<button type="submit">Save</button>
</form>

$(document).on("submit",".save",function(e){
e.preventDefault();
$.post($(this).attr("action"),$(this).serialize(),function(r){
//result
alert(r);
});
});

$item = $_POST['itemName']

foreach( $item as $key => $val ) {
  //iterate itemName values
}