A bounty program, an airdrop, a campaign,... are sometime the same method or not for free token distribution. A bounty usually request to follow fb group, twitter, reddit, YT channel, Telegram,... Generally, it's very good way to earn free tokens. You can find the bounty program through the bitcointalk forum and many different social forums...
Yes maybe they are all the same method but they differs to the token being distributed because thtat would matter what type of bounty campaign which differs. The token is really competitive to the value that raising it. Their re a lot of bounty camapign you can choose what is the best of it.