An NFC tag is a small, wireless device that uses Near Field Communication technology to transmit data. These tags can store information such as URLs, contact details, or product information, and can be read by compatible devices like smartphones when they are brought close together. NFC tags are often used in various applications, including marketing, access control, and payment systems. They are typically passive devices, meaning they do not require a power source and can be activated by the electromagnetic field generated by an NFC reader.