A rewriting system is a program that takes a sentence or a group of words and turns it into a different sentence or group of words. It does this by changing the words and putting them in a new order. For example, if you have the sentence "I like to eat apples," the rewriting system might turn it into "Apples are delicious when eaten by me." By changing the words and rearranging them, you can change the meaning of the sentence.