The allContent variable is a default prop loaded by the Plenti generator automatically. It holds the field values for every piece of content on your site. This is very handy for creating lists, or creating aggregate pages such as a "blog posts" landing page or "recent news" page. 

Filter allContent to get a specific type

By default allContent holds everything from your "content" folder. You can filter this to get a list of a particular type of content, like blog for example: 

{#each allContent as content}
  {#if content.type == blog}