Social Cards are visible on social media networks and are the combined results of using:
A social card is what you see as a "card" style display on the social channel itself and is a way to engage your audience with eye-catching, impactful content.
Social cards include usually include the link-post social image size because this social media image size is ideal for posting with a content update, and are the standard for when links are shared hence the name “link posts.”
The best size is 1200 x 628 as it works well for Facebook, Twitter, Linked and also appears correctly on Google.