A definition of a card (on the web) by Khoi Vinh:

A card is a single unit of content or functionality, presented in a concise visual package. More advanced cards use that form to surface content or functionality from other apps, and allow users to interact with that content or functionality directly in the context of where a user encounters the card.

Think embeddable tweets for example. Speaking of: those Twitter Cards just got taken to the next level as it’s now possible to make a purchase directly from within the card (pictured above)!

What is a card? →

Spotify Play Button

This should work:

Too bad it opens up Spotify, instead of streaming the audio inline. But on the other hand, I can think of many reasons why that’s disabled.

And way too cool that the embedded player actually follows along with progress meters and playing indicators as you progress listening a track and/change it in Spotify (the app) itself.

Spotify Play Button →