A whitelist is a list of entities, such as IP addresses, email addresses, domain names, or URLs, that are approved or allowed by the owner, the administrator, or the user of a system, a network, or an application, to access, to use, or to receive certain services, resources, or data, based on the policies, the rules, or the criteria that are defined by the owner, the administrator, or the user of the system, the network, or the application. A whitelist is a security, a privacy, or a filtering mechanism that is used to protect, to authorize, or to control the access, the use, or the sharing of the services, the resources, or the data, by only allowing the entities that are specified in the whitelist, and by blocking, by warning, or by challenging the entities that are not specified in the whitelist. A whitelist is often used in combination with a blacklist, which is a list of entities that are not approved or not allowed, in order to provide a more comprehensive, more flexible, and more effective security, privacy, or filtering mechanism.