SSL (Secure Sockets Layer) is the predecessor of TLS (Transport Layer Security). SSL is technically obsolete and insecure – all modern connections use TLS. However, the term "SSL" is still commonly used even when TLS is meant. When you see the padlock icon in your browser, your connection uses TLS.
An SSL/TLS certificate serves two purposes: it authenticates the identity of a website and enables encrypted communication. The certificate is issued by a trusted Certificate Authority (CA) and contains the domain name, the CA's signature and an expiry date.
Let's Encrypt is a free, automated and open Certificate Authority. It issues DV certificates valid for 90 days that can be renewed automatically with Certbot. Let's Encrypt is trusted by all major browsers and is used by millions of websites.
SSL/TLS is the encryption technology behind HTTPS. It authenticates websites and encrypts data in transit, protecting against eavesdropping and man-in-the-middle attacks. TLS 1.3 is the current standard. Free certificates from Let's Encrypt have made HTTPS accessible to all websites. Always check that websites you share sensitive data with use HTTPS with a valid certificate.