What is the difference between HTTP and HTTPS?

HTTPS (HTTP Secure) is HTTP over TLS/SSL, encrypting data in transit. HTTP sends data in plaintext, vulnerable to eavesdropping and man-in-the-middle attacks. HTTPS uses port 443 (HTTP uses 80). HTTPS provides: encryption (confidentiality), integrity (data not modified), authentication (server identity via certificates). Modern browsers flag HTTP sites as insecure. HTTPS is essential for login pages, payments, and now recommended for all sites.