Uncaught ReferenceError: $ is not defined

Uncaught ReferenceError: $ is not defined

hi I tried to execute this code but its not working....
here is the code. 

  1. <!DOCTYPE html>
    <html>
    <head>
    <title>Testing Dropbox</title>
    </head>
    <body>

    <div>
        <textarea class="carPark"></textarea>
    </div>
    <div>
        <select class="carDealer">
            <option value="volvo">Volvo</option>
            <option value="saab">Saab</option>
            <option value="mercedes">Mercedes</option>
            <option value="audi">Audi</option>
        </select>
    <script>
    function textareaValue(m){
    $(".carPark").val(m.target.value);
    }
    $(".carDealer").on("change", textareaValue);
    </script>
    </div>


    </body>
    </html>



it shows "Uncaught ReferenceError: $ is not defined(…)", can't figure it out, could you please help me?