What are cryptocurrency airdrops?

Could you elaborate on the concept of cryptocurrency airdrops? I've heard the term mentioned frequently in the crypto community, but I'm still unclear on the specifics. Is it a promotional tactic or a way to distribute tokens? How do they work, and what are the potential benefits and risks for investors? Additionally, are there any requirements or qualifications that need to be met in order to participate in airdrops? Understanding the mechanics of airdrops seems crucial in today's fast-paced and highly competitive cryptocurrency market.