ThinkGear is the name of NeuroSky's single dry sensor technology that allows the measurement, amplification, filtering, and analysis of EEG signals and brainwaves. Combined with NeuroSky's proprietary eSense™ algorithms, this allows a headset to be able to measure the wearer's state of mind, and makes this information available to applications so that the applications can respond to your mental activity.
For more information, please refer to http://developer.neurosky.com/docs/doku.php?id=what_is_thinkgear