Purpose of evt in jQuery event function

Question

What is the purpose of using the (evt) here? It seems to work just fine with leaving it empty, like highlight(). also, the alert doesn't include anything.

<script>
$(function (){
    $("#height").html($("#theDiv").height());
    $("#theDiv").on("mouseover mouseleave", highlight); 
});

    function highlight(evt) {
        $("#theDiv").toggleClass("change");
        alert(evt);
    };  
</script>