The rulebook:
"After you have completed all the actions you choose, you must reduce the cards in your hand to eight or less. If you have eight or fewer cards in your hand, then you should announce that you are finished. If you have more than eight cards in your hand, then you should reduce the cards in your hand down to eight or fewer by discarding cards from your hand face up on the top of your discard pile."
The number is always paired with "less" or "fewer", so you can discard to 7, or 3, or 0.4, or whatever you want, as long as it's no more than 8.
