Hey what are event and progress in function body from function(event, progress, stepValue)?

$(".circle .bar")
    .circleProgress(options)
    .on(
        "circle-animation-progress",
        function (event, progress, stepValue) {
        $(this)
            .parent()
            .find("span")
            .text(String(stepValue.toFixed(2).substr(2)) + "%");
         }
     );