HTTP is the HyperText Transfer Protocol.
The http kioslave is used by all KDE applications to handle connections to HTTP servers, that is, web servers. The most common usage is to view web pages in the Konqueror web browser.
You can use the https kioslave in Konqueror by giving it a URL.
https is http encapsulated in a SSL/TLS stream.
SSL is the Secure Sockets Layer protocol, a security protocol that provides communications privacy over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery.
TLS stands for Transport Layer Security.