Airdrop is the free distribution of crypto coins or tokens to the wallets of users. It may be done to increase the awareness of the company and its coin. Or as a reward to users or subscribers. Or to maintain the stability of the coin. The benefit is it ensures coins are evenly distributed and truly decentralized.
It may also be a fundraising process. Airdropping for this purpose can raise the market value of the coin without even selling a single coin.
It is actually free money being distributed but in the long run, it brings many more benefits to the company.

This feature is nowadays integrated by many cryptocurrency platforms developers along with other features such as multi-wallet, etc.
You can read about more such features offered in a crypt exchange at
https://www.epixelmlmsoftware.com/cryptocurrency-exchange-software

Anybody can get involved in airdrop if they confirm the following, a cryptocurrency wallet, base tokens, and obviously, access to information.