For content that is only tangentially related, or that serves a separate purpose than the surrounding flow, the aside element should be used (and can itself wrap a figure)...html5.1 Nightly
The figure element represents some flow content, optionally with a caption, that is self-contained (like a complete sentence) and is typically referenced as a single unit from the main flow of the document...html5.1 Nightly
The element can thus be used to annotate illustrations, diagrams, photos, code listings, etc.
When a figure is referred to from the main content of the document by identifying it by its caption (e.g. by figure number), it enables such content to be easily moved away from that primary content, e.g. to the side of the page, to dedicated pages, or to an appendix, without affecting the flow of the document.
If a figure element is referenced by its relative position, e.g. "in the photograph above" or "as the next figure shows", then moving the figure would disrupt the page's meaning. Authors are encouraged to consider using labels to refer to figures, rather than using such relative references, so that the page can easily be restyled without affecting the page's meaning.
The figcaption element should be used to describe the contents of the figure or accompanying text that you want to include with the figure .
The figcaption element represents a caption or legend for the rest of the contents of the figcaption element's parent figure element, if any.html5.1 nightly