Rate Of Investment, so like if you bid 5$ and get an upvote of 9$ you'll get a decent ROI. There are many bid bots underneath the main ones there where you can make much smaller bids yes. You won't get much it's like if you bid 0.50 you may get a 1-1.50$ upvote. Keep in mind the payout is split up into several parts for curation and author then into sbd, steem, power.