:someone or something whose abilities or characteristics are not yet known（能力或特点）尚未被人所知的人（或物）
If you've never been published before, you're an unknown quantity, so you're going to have difficulty selling your first novel.如果你之前从未发表过作品，你就是一位尚不知名的作者，因此要卖掉你的第一部小说将是有难度的。