Open Graph (OG) is the metadata protocol that lets a page control its social-share preview: the title, description, image, and type that LinkedIn, Facebook, Slack, Discord, and most other platforms render when a user pastes the URL. Set via <meta property="og:title" content="...">, og:description, og:image, og:url, og:type.
The single most important OG tag is og:image -- a 1200x630px image that anchors the preview. Without it, social previews fall back to a tiny site favicon or no image at all, drastically lowering click-through. Every public page should ship a meaningful OG image; static pages get a designed card, dynamic pages (per-product, per-article) get a templated card with the entity name overlaid.
Twitter has its own protocol (<meta name="twitter:card">) but Twitter's parser falls back to OG tags when Twitter-specific tags are missing, so OG covers most of the surface.