ICO is the abbreviation of Initial Coin Offering
It refers to a sale of a limited number of Tokens or Coins before the actual Crowdsale Pre-sale are in many cases conducted when the actual technology behind the Tokens is not yet deployed Usually the price of token is lower in a pre-sale than a Crowdsale Prime goal is to create awareness and raise some capital to allow the project to grow
This is the final stage of the ICO where tokens are available publicly to all investors.