Clarification on what a "class" is


#1

When a div points to a "class" - what is this (a class)?
<div class="jumbotron"> for example


#2

You can set your DIV to be a class or an ID. ID is unique and class is generic, it can be used by a lot of DIVs.

<div id = "myWebPage">

  <div class = "post">
     Your text goes in here
  </div>

  <div class = "post">
     Your text goes in here
  </div>

</div>

You will use a lot of classes when you start Bootstrap classes.