In more detail
The protocol came from Facebook and is now read by most platforms that build link previews, including LinkedIn, Slack, WhatsApp and Discord. The core tags are og:title, og:type, og:image and og:url, with og:description and og:site_name commonly added. A share image of about 1200 × 630 pixels (a 1.91:1 ratio) with absolute URLs gives the best preview. X (Twitter) reads its own twitter: tags, such as twitter:card, and falls back to Open Graph for most of the rest.
Why it matters
Without the tags, platforms guess, often picking a logo, an advert or no image at all. Relative image paths fail because the crawler fetches the image on its own. Platforms also cache a preview the first time a link is shared, so a corrected image may not appear until that cache is refreshed.
Example
<meta property="og:title" content="How DNS works">
<meta property="og:description" content="From typing a name to getting an IP address, step by step.">
<meta property="og:image" content="https://example.com/img/dns-share.png">
<meta property="og:url" content="https://example.com/guides/dns/">
<meta property="og:type" content="article">
Common confusion
The meta description feeds search results; Open Graph feeds social previews. Most pages set both, often with similar wording.