In the context of blockchain and cryptocurrencies, a whitelist is commonly used to allow only pre-approved participants to access an initial coin offering (ICO), token sale, or other sensitive actions. This mechanism helps to filter out unwanted participants and mitigate risks such as fraud, bots, or other malicious activities. Entities or individuals usually need to go through a verification process to get added to the whitelist, which can include tasks like identity verification or KYC (Know Your Customer).