What is back propagation in the novel, Galatea 2.2?

Back propagation is the process by which information is put into a computer, and run through a program. If the information that is put out at the end of the process does not match the trainer's output, through the trainer's own independent process, the correct answer is submitted to the process, and the information is sent through again, in hopes that it will result in the same answer as the trainer's. Richard explains this process as a way to defend himself against Lentz's aggressive conversational style.