The protocol used for secure data transmission over the internet is known as HTTPS, which stands for Hypertext Transfer Protocol Secure. HTTPS employs SSL/TLS encryption to ensure the confidentiality and integrity of data exchanged between clients and servers. This protocol not only protects sensitive information, like passwords and credit card details, during transmission but also verifies the authenticity of the communicating parties. HTTPS is essential for secure web browsing, fostering user trust while navigating online services and e-commerce platforms.