What are these twitter cards?

I see big accounts promoting twitter cards.. what are they? How do they get paid off of them?

Twitter cards are one of Twitters advertising assets. You can use a card to display a photo of your product with a call to action button such as show now or view more. The cards are clickable which alleviates the need to have a tweet with a URL in it thus the thought is this leads to a higher CTR. They make money like a normal PPC advertiser would, by spending less on ads than revenue generated by clickers.

They are the same as big accounts posting ad links, just in the form of twitter cards as cards generally tend to generate more clicks.