Discoverability: the ability to look at something and discover what operations one can do.
Examples of discoverability:
a cable port on a computer
a tape dispenser
a pepper pot
computer trackpads (an example of where there is no discoverability)
Feedback: a signal of what happened.
Examples of feedback:
a light or sound when you plug the computer cable into the port
a sound or feeling when you use the stapler
a sound when you remove tape from the dispenser
a sound or feeling when you use the pepper pot.