The noise floor refers to the RF energy present in an environment from both intentional and unintentional RF radiators. This forms the baseline level of RF energy that the signal from any intentional transmitter, such as a WLAN, must rise above to be distinguishable. It includes various sources of interference in the RF spectrum, but it is not specifically caused by devices like elevators or microwaves, nor is it extra energy radiated by access points and client devices.