An RFID card (Radio Frequency Identification card) is a small, portable device that uses radio waves to communicate with a reader. It typically contains a microchip and an antenna, allowing it to transmit data wirelessly. RFID cards are commonly used for access control, payment systems, and inventory management, providing a convenient way to identify and track items or individuals. These cards can be passive, active, or semi-passive. Passive RFID cards do not have their own power source and rely on energy from the reader, while active RFID cards have a battery and can transmit signals over longer distances. Semi-passive RFID cards have a battery but only activate when in range of a reader.