sport["name"] 是什么意思

   
        <script type="text/javascript">
            $(function () {
                $("#btnShow").bind("click", function () {
                    var $this = $(this);
                    $.getJSON("http://www.imooc.com/data/sport.json",function(data){
                        $this.attr("disabled", "true");
                        $.each(data, function (index, sport) {
                            if(index==3)
                            $("ul").append("<li>" + sport["name"] + "</li>");
                        });
    
                    });
                })
            });
        </script>

上面的js代码中 sport["name"] 一部分不理解。之前看到有人说是为了转化为字符串？？？这个语法是怎么定义的呢？？求解