Here’s the text of a sample posting in Quote format.  Under the Twenty Eleven theme (as usual), this format is rendered in the same way as a Standard form posting, except that it adds the heading “QUOTE” above the post title in the entry for this post that appears in the main blog page and applicable archive pages.

What http://codex.wordpress.org/Post_Formats says about this format:

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.