Post Formats is a theme feature introduced with Version 3.1. A Post Format is a piece of meta information that can be used by a theme to customize its presentation of a post. The Post Formats feature provides a standardized list of formats that are available to all themes that support the feature. Themes are not required to support every format on the list. New formats cannot be introduced by themes or even plugins. The standardization of this list provides both compatibility between numerous themes and an avenue for external blogging tools to access this feature in a consistent fashion.

• aside – Typically styled without a title. Similar to a Facebook note update.
• link – A link to another site. Themes may wish to use the first <a href=””> tag in the post content as the external link for that post. An alternative approach could be if the post consists only of a URL, then that will be the URL and the title (post_title) will be the name attached to the anchor for it.
• image – A single image. The first <img /> tag in the post could be considered the image. Alternatively, if the post consists only of a URL, that will be the image URL and the title of the post (post_title) will be the title attribute for the image.
• quote – A quotation. Probably will contain a blockquote holding the quote content. Alternatively, the quote may be just the content, with the source/author being the title.
• status – A short status update, similar to a Twitter status update.