What is Let's Encrypt?
If you want to make sure that traffic between your website and the wide world is encrypted, you need to install an SSL Certificate. Traditionally SSL certificates for your domain can be quite expensive, and are often only used for sites where personal details are held, or payment transactions are taking place. Let's Encrypt has the potential to make the whole internet secure, by providing a Certificate Authority service for free.
Visit the Let's Encrypt site to learn more.