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This post is formatted as a Gallery.  It uses the Format box on the edit post page.

Being a Gallery it can be shown in a TwentyFourteen Ephemera widget.  Use this widget to list your recent Aside, Quote, Video, Audio, Image, Gallery, and Link posts.

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.

from: Post Formats « WordPress Codex