Edit in JSFiddle

$(document).ready(function () {
                $("#myDiv").hover(function () {
                    $(this).html("Mouse pointer entered the div. This text will disappear as you move out of the div.");
                }, function () {
                    $(this).html('Hover ME !');
                });
            });

<html>
        <head>
        <title>HTML</title>
        </head>
        <body>
        <div id="myDiv">Hover ME !
        </div>
        </body>
        </html>

#myDiv
        {
        background-color:gray;
        margin-left:100px;
        width:200px;
        height:200px;
        font-family:comic sans ms;
        }