RFID uses electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically stored information. 
 
Put simply, RFID is similar to barcode technology but uses radio waves to capture data from tags (or RFID labels), rather than optically scanning the bar codes on a label. An RFID scanner does not require the tag or label to be seen to be able to read its stored data, but of course a label may be printed with a barcode and other text. An RFID printer programs the RFiD chip in a label and also prints text and/or barcodes on the label.

RFID is similar to barcodes, except that:
RFID labels can be read without being visible. (Unlike barcodes, RFID does not require "line of site").
RFID labels can be written to as well as read. (Typically when printing the label, the tag is also programmed).

RFID Frequencies
Two different frequencies are available for smart labels - ISO 18000-3 High Frequency (HF or 13.56 MHz) or ISO 18000-6 Ultra High Frequency (UHF ISO or Gen2). Typically hardware suitable for use with one frequency will not work with the other.