SSL stands for Secure Sockets Layer. It is the standard technology to keep an internet connection secure, safeguarding any sensitive data that is being sent between two systems, can be server to server or a server and a client, preventing criminals from reading and modifying any information transferred.
SSL uses encryption algorithms to scramble data in transit, makes sure that any data transferred between users and sites, or between two systems remain impossible to read, preventing hackers from reading it as it is sent over the connection.
TLS (Transport Layer Security) is an updated, more secure, version of SSL. Not only is TLS more secure and performant, most modern web browsers no longer support SSL 2.0 and SSL 3.0. While SSL is still the dominant term on the Internet, most people really mean TLS when they say SSL.
HTTPS (Hyper Text Transfer Protocol Secure) appears in the URL when a website is secured by an SSL certificate. The details of the certificate, including the issuing authority and the corporate name of the website owner, can be viewed by clicking on the lock symbol on the browser bar.