rel="noopener" is a link attribute that prevents the destination page from accessing the parent window via the window.opener JavaScript reference. Required as a security best practice on any link with target="_blank" — without noopener, the destination page can navigate the parent window (a known phishing vector called tabnabbing).
Most modern browsers (Chrome 88+, Firefox 79+, Safari 12.1+) implicitly apply noopener to target="_blank" links, but explicit rel="noopener" is the cross-browser-safe posture. Pair with rel="noreferrer" when you also want to prevent the destination from seeing the referrer URL.
Important: noopener is NOT nofollow. The two attributes serve completely different purposes. noopener is for security (preventing tabnabbing); nofollow is for SEO (preventing link equity passage). A link can have noopener without nofollow and vice versa.
For embed badges and similar shareable backlinks, the correct posture is rel="noopener" WITHOUT nofollow — security against tabnabbing, but full link equity passage to the destination. SeoChatAI's badge snippets follow this pattern.