Http stands for Hyper Text Transfer Protocol. It allows World Wide Web users to transfer information like image, text, video, music, graphic and other files on web pages. 

HTTPS stands for Hypertext Transfer Protocol Secure. HTTPS is a protocol which uses an encrypted HTTP connection by transport-layer security. 

The major difference between HTTP and HTTPS is that HTTPS is a secure encrypted connection transaction. You may see the word "secure" with the HTTPS connection because it is secure. All your files, data tranfers etc are secure with an https while on the http, they are not.