HTTPS is the encrypted version of HTTP. Instead of using plain-text socket communication, HTTPS encrypts the session data using either a version of SSL (Secure Socket Layer) or TLS (Transport Layer Security) the IETF-standardized successor to SSL, thus ensuring reasonable protection from eaves-droppers, and man in the middle attacks.
Its default TCP/IP port is 443.
Of course the level of protection depends on the correctness of the implementation by the web browser, and the server software; and the actual symmetric and asymmetric encryption algorithms and hash algorithmss supported.