Radio Frequency Identification (RFID) was invented more than 50 years ago but has so far failed to live up to its promise to connect everyday things through a wireless network and make it possible, in theory, to track every item ever produced.
Computer scientists dub RFID "The Internet of Things," in which anything from shampoo bottles to marathon runners can be tracked using radio tags. Criticism from some camps is that the technology can lead to an unacceptable invasion of privacy.
Wikipedia provides a detail explaination on RFID. Click here.
Small business computing.com also provide a brief definition here.
The Free Dictionary.com - here.
Finally, a blog specialised on RFID which worth looking into.