HTTPS
HTTPS is an encrypted version of HTTP: it uses TLS to encrypt the communication between the visitor's browser and your server.
With HTTPS, what travels between the browser and the server cannot be read on the way. A site that uses it shows it in the address.
Why it matters for a small business
A form, a booking or a login on your site sends people's details. HTTPS protects them in transit. Check that your site address starts with https.
Source: MDN, 'HTTPS - Glossary'
Related