RFID (Radio-Frequency Identification) is a technology that uses radio waves to identify and track objects, typically through a RFID tag or RFID card, which is a small device that contains a microchip and an antenna. The RFID reader/writer, also known as an RFID interrogator, emits radio waves and receives signals from the RFID tag or card, which allows it to read and write data to the tag or card. RFID cards typically have a unique identification number that can be used for various purposes, such as access control, inventory management, and asset tracking. They can be passive, which means they have no power source and rely on the energy from the RFID reader to function, or active, which means they have a power source and can transmit a signal back to the reader.