About Qi Wireless Charging:

Qi (pronounced “chee”) is an interface standard developed by the Wireless Power Consortium (WPC) for inductive electrical power transfer (up to 120 W) over distances of up to 4 cm (1.6 inches). The wireless power transfer occurs through electromagnetic induction meaning that the required power reaches the device not through a traditional cable, but rather wirelessly through the use of electromagnetic fields.In order to charge devices wirelessly, you basically need a Qi Transmitter (for example a charging pad / station) and a Qi Receiver (e.g. a case or a smartphone which has Qi integrated). The idea behind Qi is that you can use any Qi Transmitter together with any Qi Receiver for charging your device wirelessly.

If you want to find out more about technical details etc., then you may have a look at the official website of Qi, which you can find here.