Short definition

SSL certificate — a digital certificate that lets a browser authenticate a domain and establish an encrypted TLS connection.

Also known as: TLS certificate, HTTPS certificate.

An SSL certificate lets a browser verify that it is connected to the intended domain and establish an encrypted connection. Modern HTTPS uses TLS; “SSL certificate” is a legacy name.

How does an SSL certificate work?

An SSL certificate binds a domain name to a public key. When a visitor connects, the server presents the certificate, and the browser checks its certificate chain, validity period, and domain name. If those checks succeed, the browser establishes an encrypted TLS connection. Many hosting platforms renew certificates automatically, helping prevent expired-certificate outages.

What does this mean for a small business?

Browsers warn visitors when a site uses unencrypted HTTP. Form submissions, quote requests, and contact details should be sent over an encrypted connection. Most hosting providers include free certificates, so HTTPS is mainly a matter of correct configuration rather than cost.

What should you watch for with an SSL certificate?

  • enforce HTTPS for every visitor, with a redirect from plain HTTP;
  • avoid mixed content, such as images or scripts loaded over plain HTTP;
  • let the certificate renew automatically and monitor expiration;
  • check that the certificate covers every hostname visitors use;

How it relates to other website choices

An SSL certificate is usually configured through web hosting and managed through routine website maintenance. A CDN also needs a valid certificate to serve the site over HTTPS.

Reliable source and further reading

For the technical foundation, read MDN on HTTPS.