HTTPS is a protocol that combines HTTP with SSL/TLS encryption to provide secure communication between a client and server. It encrypts data sent between a browser and website using a public/private key system. When a client requests an HTTPS connection, the website sends its SSL certificate containing a public key. This begins the SSL handshake where shared secrets are generated to uniquely encrypt the connection. HTTPS is important for securing sensitive communications and establishing trust, as it is used widely on banking, payment, shopping and email sites.