do you remember when you want to do a post, you have the options of power up 100%, 50%/50% payout and decline payout? That is what it means by declining payout and return it back to the pool of steemit ecosystem. This is normally used when people want to make an annoucement and will decline payout after 7 days from any upvotes. The system is fair, so here we are trying to be fair to the communities and to the newbies to encourage them to post more and more.