How does airdrop work?

Could you possibly elaborate on the mechanics of an airdrop? I'm quite fascinated by the concept but am having trouble grasping the intricacies. Could you break it down for me? How does the distribution process occur? Are there specific criteria that need to be met by recipients? And what are the benefits for both the issuer and the recipients? I'm eager to learn more about this intriguing aspect of the cryptocurrency world.