A "whitelist" is a list of approved items, such as email addresses, IP addresses, or applications, that are granted access to a system or network. This concept is commonly used in cybersecurity to enhance security by allowing only trusted entities while blocking all others. In contrast to a blacklist, which identifies harmful or unwanted items, a whitelist focuses on what is permitted. For example, in email filtering, a whitelist can ensure that messages from known contacts are delivered, while those from unknown sources may be blocked or flagged as spam.