Load Modulation is a method of conveying a signal from one device to another by means of modulating the load that the transmitting device imposes on a radio signal provided by the receiving device.
This is used, for example, to allow ISO/IEC 14443 and ISO/IEC 15693 NFC cards to reply to the reading device without the need for the NFC card to contain a power source. Instead, it is powered by the radio signal provided by the reader and it conveys its data back to the reader by modulating the load that the NFC card imposes upon the Reader's radio signal.[1] [2]