Final answer:
Flat characters are static and do not change, while round characters are dynamic and undergo development or transformation.
Step-by-step explanation:
E.M. Forster proposed the distinction between flat and round characters in his book 'Aspects of the Novel'. Flat characters are static and do not change throughout the story, while round characters are dynamic and undergo development or transformation.
For example, a flat character could be a villain who remains evil from the beginning to the end of the story, while a round character could be a protagonist who learns from their mistakes and grows as a person.