If you've been around cryptocurrencies for a while you've probably woken up one day and found that some strange named tokens had been deposited to your Ethereum address. You go to Google and check these tokens and find they're listed on a relatively obscure decentralized cryptocurrency exchange. When you verify the order book you find that everyone is dumping the token as quickly as they arrive. What just happened? Well, you've just been graced by an airdrop.
Airdrops are carried out for various reasons. A cryptocurrency creator with small marketing budget may want to get his coins out there, even if it means distributing some of them for free. Others may want to spend some of the initial supply of coins on marketing instead of paying fiat money for promotion. The general idea is to make money for the coin creators by distributing a small amount of coins or tokens and expecting this to generate trade volume on exchanges.
So, in essence, yes it's a kind of "free lunch" for recipients. An older concept of airdrop would be the faucet. Back in the day there were sites where you'd paste your Bitcoin address and it'd send you free Bitcoins. Yes, whole Bitcoins, lots of them given away for free during the early days of cryptocurrencies. Obviously legit Bitcoin faucets are no longer a thing and today they're but honeypots for ad clicks. In fact Google has banned faucet sites from publishing AdSense ads, due to the sheer amount of such sites and their fake coin distribution.
Having said this, there have been successful airdrops. DeepOnion (ONION) were given out for free and they're worth U$ 1,30 at the time of this writing. Ethereum Dark (ETHD) were also airdropped and are now worth 6 cents of a dollar and NEM (XEM) which is now worth a quarter of a dollar! These are 100% free lunch. Anyone who received ONION and held onto it made some real good money from their patience.
We hope this brief intro to airdrops has given you an idea of this interesting cryptocurrency phenomenon. Keep in mind that most of the time the old adage remains true "there is no such a thing as a free lunch". But it's the cryptocurrency world and anything is possible. Airdrops are free, so if you see one all you can lose is a few minutes of your time to earn some free tokens/coins. Can't hurt to try.