Definition

An SSL certificate (today almost always a TLS certificate) is a file issued by a certificate authority that proves a site's identity and supplies the public key used to set up an encrypted connection between a browser and a server.

The protocol in use is technically TLS — SSL was deprecated years ago — but the certificate is still commonly called an SSL certificate. A valid certificate is what allows a URL to load over `https://` with a padlock in the address bar. Google has confirmed HTTPS is a lightweight ranking signal and modern browser features (service workers, geolocation, payment APIs) require a secure origin.

Examples

• Let's Encrypt on a small site

  A small business installs a free Let's Encrypt certificate and configures auto-renewal. Browsers stop showing a "Not Secure" warning and the site can now serve resources over HTTPS without mixed-content errors.

• Expired certificate

  An SSL certificate lapses without renewal. Browsers display a full-page interstitial warning and refuse to load the site, traffic collapses, and Search Console flags the URLs as unreachable.

Sources

• web.dev — Why HTTPS matters
• Google Search Central — Secure your site with HTTPS

Related terms

• HTTPS
  Hypertext Transfer Protocol Secure — the encrypted version of HTTP. Google uses HTTPS as a lightweight ranking signal.
• Mixed Content
  A page loaded over HTTPS that also loads sub-resources — images, scripts, stylesheets — over insecure HTTP, weakening the security of the original page.
• Page Experience
  Google's umbrella term for signals describing how users perceive a page — Core Web Vitals, HTTPS, mobile usability, and absence of intrusive interstitials.

Where QueryCatch uses this

• SEO Audit