Intval () in php

I have a piece of code that is used in Datatables server side, and I do not know what this function is for, since it is inside the answer, but not in the library.

$output = array(
    "draw" =>         intval($_POST["draw"]),
    "recordsTotal" => get_all_data($cnn),
    "recordsFiltered" => $number_filter_row,
    "data" =>  $rst

);