A card is a short summary of the most important things to know about a topic. A card should be short enough to fit on a phone screen, and can link to other cards to provide information beyond what fits on one card.
A card is not a wiki. Each card is only editable by its owner, but other people can use comments to suggest changes to the card.
Cards can contain links, images, and footnotes. Each card is either published by a publication, or is unlisted.