Post format which is about post display style, the tumblr style for:

• Standard – Just your typical post.
• Image – A single image. You can either upload an image or enter an URL.
• Gallery – A series of images.
• Link – A link to another website.
• Video – A single video. You can upload a video or enter a video embed code or URL.
• Audio – An audio file. Upload a file or paste an audio embed code into the box.
• Chat – A chat transcript. Just copy and paste it into the editor.
• Status – Much like Facebook or Twitter, a short status update.
• Quote – A quotation.
• Aside – A quick thought or idea.

They are has been decided to remove from the core version for next release of 3.6 which is now taking several weeks to go.

According to WPMU news said that Mark Jaquith announced that Post Formats UI will not be a part of the core in WordPress 3.6 but will be relegated to a plugin, similar to MP6.