RFID is short for “Radio Frequency IDentification” and is used to track goods and packaging via small embedded chips. These things are everywhere: clothing, food, passports - basically everything that’s able to carry the “dust” sized chips (at the time of writing, Hitachi holds the record for smallest RFID at 150 x 150 x 7.5 microns).
Why should you worry about this? Because RFID not only tracks the product, but also the buyer - a fact that can be exploited by marketers, government agencies, and criminals. Apparently Benetton tried to sew millions of RFID tags into women’s garments in 2003 - a plan that was successfully boycotted by consumer group CASPIAN. Educate yourself about RFID at FoeBud or Wikipedia.