Cards are "a user-interface (UI) container for short or related pieces of information ref " which there are currently two formats for, MessageCards and AdativeCards . The underlying data format is a JSON object that describes the content to be rendered by a supporting client. Eg here is a basic sample So they are a simple way of presenting information in consistent manner which then makes deploying that same UI experience across multiple client forms factors (mobile,web,desktop) a lot easier. Cards also allow you to define actions, so then the cards themselves can become a small app or part of an integration piece of a Line of Business workflow etc. Actionable Cards in Outlook have the ability to link with an Outlook Addin's see which starts to really extend what you can use cards for. This means your no longer just stuck in the limited feature set of Cards but you can use the richness available in the Outlook Addin framework . Email Security Cards rel y o...
Pushing the Envelope in Messaging and Office 365 Development