Too Long; Didn't Read
IGO stands for Initial Game Offering. It's similar to ICO – Initial Coin Offering and IDO – Initial DEX Offering. It’s a presale of tokens (available to pre-selected buyers) before they are listed on an exchange. While ICOs and IDOs can be for any type of token/project, IGOs, as the name implies, are only crypto games.
The purpose of the IGO is to raise funds for the next stages of the game’s development, marketing, etc. This means investing at a very early stage and of course, this carries some risks as there’s no guarantee that the project will be completed or successful. However, the benefit of investing so early is that you’re buying the token at the lowest possible price and as a result, you can expect the value of the token to go up significantly (5x – 60x in my experience) within the first 48 hours... and potentially even more in the future.