The term RFID refers to the technology. The tags should properly be called "RFID tags".

 

There are three types of RFID tags: passive RFID tags, which have no power source and require an external electromagnetic field to initiate a signal transmission, active RFID tags, which contain abatteryand can transmit signals once an external source ('Interrogator') has been successfully identified, and battery assisted passive (BAP) RFID tags, which require an external source to wake up but have significant higher forward link capability providing greater range.

 

There are normally three ranges of RFID frequency: Low Frequency (LF), High Frequency (HF) and Ultra-high Frequency (UHF). Different class covers different range of frequency, one most importance of the frequency is that determines the reading distance of tags and this distance directly determine the application of the frequency to certain applications.

 

Low Frequency is talking about 125 KHz to 135 KHz.

High Frequency is talking about 13.56 MHz.

Ultra High Frequency is talking about 860 MHz to 960 MHz.

 

There are various international standards governing the use of this emerging technologies, making sure the products and solutions would be eventually compatible to certain extent.