Comprehensive and Detailed Explanation From CEH v13 Guide:

R-U-Dead-Yet? (RUDY) is a DoS tool that targets web applications by sending slow HTTP POST requests with large Content-Length headers. This consumes server resources, leading to a denial of service.

CEH v13 Reference:

Module 9: Denial-of-Service – DoS Tools

“R-U-Dead-Yet? (RUDY) sends long-form POST requests to consume server-side sessions and exhaust resources without completing the transaction.”