Final answer:
The WLAN security approach designed to conceal a WLAN's existence is SSID hiding. SSID hiding disables the network's visibility in the list of available networks, making it less detectable to casual users.
Step-by-step explanation:
The approach to wireless LAN (WLAN) security that helps to conceal the existence of a WLAN is SSID hiding. Disabling the broadcast of the Service Set Identifier (SSID) makes it harder for casual users to discover the network as it won't appear in the list of available networks. However, it is not considered a robust security measure alone since determined hackers can still detect hidden SSIDs using specialized software tools.
Options like WEP (Wired Equivalent Privacy) and WPA2 (Wi-Fi Protected Access 2) are encryption standards designed to protect the data on the network. MAC filtering is a security access control method whereby the network administrator restricts access to the network by only allowing authorized MAC addresses. While these can improve security, they do not serve to hide the network itself.