Airdrop - free distribution of coins (tokens) from developers, sometimes as a sign of gratitude, the developer may ask to leave a comment about the project on the forum or something else, but not requiring much time and effort.
Bounty (bounty) - distribution of coins (tokens) for the work done, namely for being active in social networks (posts, likes, retweets), helping the project in the form of translating information into other languages, keeping topics on forums, moderating chats, etc.