what are prepared statements php code example

Example 1: php mysql prepare query

$stmt = $mysqli->prepare("SELECT * FROM myTable WHERE name = ? AND age = ?");
$stmt->bind_param("si", $_POST['name'], $_POST['age']);
$stmt->execute();
$stmt->close();

Example 2: php prepared statement upload file

$query = "INSERT INTO contracts(`filename`,`filedata`, `filetype`,`filesize`) VALUES (?,?,?,?)";
$stmt = $con->prepare($query);
$null = NULL;
$stmt->bind_param("sbsi", $filename, $filedata, $filetype,$filesize);
$stmt->send_long_data(1, file_get_contents($_FILES['upload']['tmp_name'])); 
$stmt->execute();