If you are a WordPress.com blogger then you may have seen the post on the Daily Post a couple of days ago about custom post types. As the article says:
Post formats add visual variety to your blog by displaying different types of content in slightly different ways.
The post includes this link to those WP.com themes that support custom post types.
But What Exactly Are Custom Post Types?
A custom post type is nothing more than a regular post with a different post_type value in the database.
The post type of regular posts is post, page use page, attachments use attachment and so on.
[From Smashing Magazine]