Pre-sale is defined as a short duration where investors can fund a cryptocurrency project before it becomes publicly available; often for a discounted buy-in price.
You may already know that an Initial Coin Offering (ICO) is when a new cryptocurrency idea becomes available for the public to invest in. A pre-sale always comes before an ICO with better prices and a lower fundraising target. Some projects need a pre-sale to support the costs of doing a big ICO.
Because a pre-sale offers better opportunities to make money than an ICO, more crypto projects are raising all the money they need in their pre-sales. Telegram, the private chat application, was supposed to have a very large ICO but instead they raised a massive $1.7 billion dollars in their pre-sale and skipped the ICO.
The downside to a pre-sale is that investors often sell their crypto on exchanges as soon as they are available for a big profit.