What is SSL / TLS / HTTPS

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are protocols that provide data encryption and authentication between applications and servers in scenarios where that data is being sent across an insecure network.

TLS is the new name for SSL. Namely, SSL protocol got to version 3.0; TLS 1.0 is SSL 3.1. TLS versions currently defined include TLS 1.1 and 1.2. We sometimes say "SSL/TLS".

HTTPS is HTTP-within-SSL/TLS. SSL (TLS) establishes a secured, bidirectional tunnel for arbitrary binary data between two hosts. HTTP is a protocol for sending requests and receiving answers, each request and answer consisting of detailed headers and (possibly) some content. HTTP is meant to run over a bidirectional tunnel for arbitrary binary data; when that tunnel is an SSL/TLS connection, then the whole is called "HTTPS".