All of the comments quoted below are wrong - these are not what airdops are!

Quote from: paxmao on February 22, 2018, 01:18:06 PM

A true airdrop will not require you to do anything, ~~except perhaps registering an Ethereum address to receive the tokens~~ (some airdrops may be new coins or based on NEO, WAVES or other platforms).

Quote from: Alluro on February 22, 2018, 01:29:15 PM

~~Some ICO projects doing airdrop campaign before launch their ICO~~. That mens they are giving their tokens for free. ~~We have do simple tasks for participate the airdrop like follow twitter, Retweet, Join telegram group etc.~~

Quote from: wandino on February 22, 2018, 01:35:55 PM

~~It's a giveaway of coins for being a part of the group or doing small tasks.~~ You can look for them on announcement threads.

Quote from: nitinkp47 on February 22, 2018, 03:19:12 PM

~~Airdrop can be the best way to get some free tokens from the community by doing simple tasks.~~
I currently participate in DeepOnion airdrops before they do full-fledged launch

This comment from MintDice (below) is the only correct answer thus far.

Quote from: MintDice on February 22, 2018, 07:58:27 PM

A crypto airdrop is when a blockchain project distributes free tokens or coins to the crypto community and to be a recipient, usually the only requirement is that you have coins from the relevant blockchain stored in your wallet. You can also get free coins from a faucet.

Cheers!

An airdrop is...

ALWAYS associated with a hard fork attempt
The release of a new coin by way of a hard fork, the forking coin needs to giveaway an amount of their coin equal to what wallets hold of the target coin (the one being forked),
and to do this they grant owners of the target coin the new coin at a specific date and time, seemingly out of thin air...thus "airdrop"

An airdop is not...

A bounty campaign
Given for doing work, e.g., performed to promote a new token release, community tasks, registration, etc.

The confusion is driven from a lot of the bounty campaigns out there - campaigns give out coins as compensation, income, for promoting the coins. And people who are new to Bitcoin and participate in these campaigns confuse the compensation that they are getting with the term "airdrop"...and then spread the incorrect use of the term.

And if you don't want to take my word for it, here's a source:

Quote from: Wikipedia entry for Airdrop (cryptocurrency)

An airdrop for a cryptocurrency is a procedure of distributing tokens by awarding them to existing holders of a particular blockchain currency.