I'd like to understand what's Airdrop and how does it different from Initial Coin Offering (ICO). Ideally in some general way.
Here are some example contexts:
The tokens will not be distributed as initial coin offering (ICO) but rather as an airdrop. "IQ Tokens will be airdropped into the EOS distribution list in late February," Forselius, told to Inverse in February 2018. Source: Wikipedia.
Blockchain-based encyclopedia startup Everipedia announced plans to distribute its IQ tokens in June through an "Airdrop" instead of taking the Initial Coin Offering (ICO) route. The move would probably help bypass increasing regulatory hitches for ICOs. Source
An airdrop is a free token distribution while a ICO is a fund offering in exchange of tokens.
Everipedia wanted to do a ICO in order to collect funds to finance their project, then Block.One made a deal with the Everipedia team by funding their financial needs and it return they build on EOS and airdrop their tokens to eos token holders.
Airdropping a token distribution to a widely distributed token distribution such as EOS can be beneficial for bootstrapping a project with a community that has an interest in the project. It also allows other projects to take advantage of the anti-consolidation properties of EOS, and achieve a more optimal distribution for their own project.