ICO is a fundraising effort to launch a new project. They are on the riskiest edge of a volatile industry as you're often giving them money before they do any (or much) work. There is a chance you get high gains from such an investment - though a greatly increased chance you will lose money.

Might be best to steer clear until you have more experience in crypto before investing. Established projects are risky enough Get a feel for making good calls first and gaining confidence that you can identify winners - an important skill if you are to fare well in the world of ICOs.

p.s. you might also hear the word Token Sale - which is the same idea..with some distinctions but by using that term the company is often trying to avoid being labeled as a security for legal reasons.