Deferred design refers to a system with the ability to be modified or tweaked later.
It best demonstrated by using programmable MicroControllers or FPGAs which are programmable. This means that they could be deployed in an application - a robot, and later programmed, or reprogrammed as is necessary. They would be able to develop a design further, and actually test in the field without the expense of recreating new hardware for each iteration.
Imagine bringing a robot to a situation that it either isn’t programmed to deal with, or finding that the programming is’t quite right. The design can now be altered, or additional design work done and coding made to adjust the robot to this situation.