SSL (Secure Sockets Layer) is a standard security technology for establishing an encrypted connection between a server and a client, typically a web server (website) and a browser or a mail server and a mail client (e.g. Outlook). SSL enables the secure transmission of sensitive information such as credit card numbers, national insurance numbers and login credentials.
When an SSL connection is established, the client and server exchange a series of messages to verify that the connection is secure. If the connection is successfully established, all data transmitted between the client and server is encrypted and secure.
SSL is used to secure online transactions and protect against data breaches. Websites that process sensitive information, such as online shops and financial institutions, use SSL to secure their connections. SSL is also used to secure email connections and is often used in conjunction with Transport Layer Security (TLS).
You can tell if a website uses SSL by the URL. Websites that use SSL have a URL that starts with "https" instead of "http". Some web browsers also display a padlock icon in the address bar to indicate that a website uses SSL.