data-toggle="collapse"——指明该元素具有折叠功能；
data-target——设置元素打开折叠后指向的元素链接。
.collapse——用来设置元素为折叠内容。
.in——设置折叠内容初始化为显示状态；
.panel-collapse——指明该元素内容为折叠面板样式。
很多其它细节请參考演示样例：
<!DOCTYPE html>
<html lang="zh_CN">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width,initial-scale=1">
<title>饭盒儿——发现身边不一样的世界</title>
<link rel="stylesheet" href="css/bootstrap.min.css" type="text/css">
<script src="js/jquery-2.1.3.min.js"></script>
<script src="js/bootstrap.min.js"></script>
<!-- HTML5 shim and Respond.js for IE8 support of HTML5 elements and media queries -->
<!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
<!--[if lt IE 9]>
<script src="//cdn.bootcss.com/html5shiv/3.7.2/html5shiv.min.js"></script>
<script src="//cdn.bootcss.com/respond.js/1.4.2/respond.min.js"></script>
<![endif]-->
<style>
</style>
</head>
<body>
<div class="container">
<a class="btn btn-primary" data-toggle="collapse" href="#collapseExample">点击查看</a>
<div class="collapse" id="collapseExample">
<div class="well">
Hello world
</div>
</div>
<hr/>
<div class="panel-group" id="accordion" role="tablist">
<div class="panel panel-default">
<div class="panel-heading" role="tab" id="headingOne">
<h4 class="panel-title">
<a data-toggle="collapse" data-parent="#accordion" href="#collapseOne">item1</a>
</h4>
</div>
<div id="collapseOne" class="panel-collapse collapse in" role="tabpanel">
<div class="panel-body">
这真是一个奇妙的站点
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading" role="tab" id="headingTwo">
<h4 class="panel-title">
<a data-toggle="collapse" data-parent="#accordion" href="#collapseTwo">item2</a>
</h4>
</div>
<div id="collapseTwo" class="panel-collapse collapse" role="tabpanel">
<div class="panel-body">
这真是一个奇妙的站点2
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading" role="tab" id="headingThree">
<h4 class="panel-title">
<a data-toggle="collapse" data-parent="#accordion" href="#collapseThree">item3</a>
</h4>
</div>
<div id="collapseThree" class="panel-collapse collapse" role="tabpanel">
<div class="panel-body">
这真是一个奇妙的站点3
</div>
</div>
</div>
</div>
</div>
<script>
// $("#accordion").on('hidden.bs.collapse',function(){
// alert("隐藏了");
// })
</script>
</body>
</html>