iBeacon is part of Apple's iOS 7, which works with low-power Bluetooth transmitters and the Apple Store app, which together track your location within a retail store, providing relevant information to your iPhone.
For example, if you were standing next to the iPhone table, with everything iBeacon requires from you enabled, it would pop a message up onto your iPhone asking if you'd like to upgrade. It would also tell you if you were eligible for getting some money back for trading in your old iPhone. It could also send push notifications to customers alerting them to when their order is ready to be picked up.
iBeacon isn't just limited to Apple Stores, either, as it has rolled out into retailers like Macy's, J.C. Penney and more.