RFC 791 is a document that defines the Internet Protocol version 4 (IPv4), which is a fundamental part of how data is transmitted over the Internet. Published in September 1981, it outlines the structure of IP packets, addressing, and routing. This protocol allows devices to communicate with each other by providing unique numerical addresses, ensuring that data sent from one device reaches its intended destination. The significance of RFC 791 lies in its role in establishing a standardized method for data exchange. By defining how packets are formatted and how they should be handled, it laid the groundwork for the modern Internet, enabling diverse devices to connect and share information seamlessly.