As you know, a block in Concrete CMS is a simple bit of content added to a page. A Block Type is the template for how those blocks are added, edited, saved, stored and displayed. Examples of block types that Concrete ships with include Content, File, Auto-Nav, Page List and YouTube video. While Concrete includes many different block types, it can't possibly include all block types that a developer might want to use for every situation. What if a client wants to place a gallery of images from flickr.com on their page, or has a custom data feed that they want to display? These are situations in which developers will likely want to create their own custom block type. Concrete makes that easy to do.