When you're flushed, your cheeks are pink. You probably look flushed after your morning jog around the block.
People become flushed from exercise, or cold weather, or embarrassment. Your flushed cheeks might give away the fact that you're nervous about your job interview or ashamed to be seen walking the dog in your pajamas. Little kids get flushed faces when they're sick, their cheeks bright and feverish. The verb flush originally meant "to fly up suddenly," and experts aren't sure how the "become red" meaning came about, although it may be a combination of flash and blush.