Edit in JSFiddle

$('dt').on('click', function () {

    function slideDown(target) {
        slideUp();
        $(target).addClass('on').next().slideDown();
    }

    function slideUp() {
        $('dt').removeClass('on').next().slideUp();
    };
    $(this).hasClass('on') ? slideUp() : slideDown($(this));

})

<dl>
    <dt><span></span>이게 뭔가요?</dt>
    <dd>나도 몰라...</dd>
    <dt><span></span>질문입니다...</dt>
    <dd>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Earum maiores.</dd>
</dl>