ICO stands for Initial Coin Offering. It's the act of raising funds by selling crypto tokens (also referred to as coins) on a blockchain-powered project. Funds are typically raised in the form of cryptocurrency such as Bitcoin, Ethereum and others.
A great advantage of raising funds via an ICO is that projects end up with not just money, but also a community of people that joined the project and care about it, they consider themselves as having invested in it. Projects that are working on a product that require user adoption, can instantly benefit, as they start with hundreds or sometimes thousands of proponents from the very beginning.
ICOs are here to stay. They enable any visionary entrepreneur to raise money no matter where they are located. It enables projects to start off with a community interested in the project's success. ICOs are open for business 24/7, they are decentralised, they make early investment liquid and they are in principle open to everyone on the planet.