A Guest Light is a LIFX light available on the Wi-Fi network, but owned and configured to another LIFX Cloud account.
When your device is connected to a Wi-Fi network with LIFX lights connected, your LIFX app will be able to access them, and turn them on and off.
However, you will only have access to these features. Renaming lights, editing them, and creating Schedules or other LIFX Cloud connections, will not be possible.
If you have setup these lights, but they appear as guest lights, please ensure you have logged into the LIFX app with the correct LIFX app email/password. If you cannot access an account that the lights were previously connected to, you can reset the light, and reconnect it to your network, using the current LIFX app account you are using.