The iCloud Activation Lock is a security feature designed by Apple to protect users' devices in case of theft or loss. When Find My iPhone is enabled, the Activation Lock is automatically turned on. This means that even if someone tries to erase the device, they will still need the original Apple ID and password to activate it. While this feature is beneficial for security, it can also pose a challenge for legitimate users who forget their credentials or purchase a second-hand device that's still locked.