In WordPress and IT security, a whitelist is a list of trusted objects or sources. Therefore if you want to allow only fours IP addresses to access your WordPress dashboard you should use the Whitelist Approach; block everyone and only allow in the four IP addresses that you trust. Whitelisting is also used when configuring for example a server or a software. For example when configuring a web server ideally you should disable all the modules and only enable those that you need. The opposite of a whitelist is a blacklist. Whitelisting is typically preferred in the security field because it is easier to manage and presents less risks.