Radio Frequency Identification. Use of small devices that can be electronically identified (and sometimes their data changed) at a distance without line of sight. Although radio is typically defined as 300 Hz to 300 MHz, nowadays the term even encompasses tags interrogated at 100 Hz and others at microwave frequencies (GHz). These devices are called tags and they may be used alone - contactless smart cards and car clickers are examples - or fitted to something in order to monitor its identity remotely. Sometimes RFID will employ tags that perform extra functions as well such as sensing what is happening or recording updated data remotely, for future remote interrogation.