A card in the context of the indieweb are small information summaries—often summaries of specific, external web pages.
For the moment, current indieweb work is focusing on developing a simpler alternative to all the silo-specific card approaches. See:
- (Apple Passbook API/format reference needed)
Examples of Facebook "cards" displays:
- link-preview for the first URL in a post
- hovercard shown when hovering the mouse pointer over someone's name, including face, name, friendship status, etc.
Google now uses cards as a method of display of various information - see the Google now page for more overall, and http://www.google.com/landing/now/#cards for examples. Some of Google now's cards appear to be produced from recommendation engines.