What is a metaphor? can you give some examples?

Elliott sent the brown-eyed children to lunch first and gave them a longer recess. The brown-eyed children could drink from the water fountain, but the blue-eyed children had to use paper cups. The change was instant, Elliott said. The children with brown eyes were suddenly more confident — and condescending

Explanation:

She wanted to show her pupils what discrimination feels like, and what it can do to people. Elliott divided her class by eye color — those with blue eyes and those with brown. On the first day, the blue-eyed children were told they were smarter, nicer, neater, and better than those with brown eyes.