There are two classifications for wireless power, non-radiative (near-field) and radiative (far-field). Near-field is employed by products that can be charged via short distances, like an electric toothbrush, RFID tags, implanted medical devices and electric vehicles. You might even have a device with Near Field Communications (NFC) that can let your device communicate with other NFC compatible devices; it’s most commonly used as a quick way to transfer data.
Near-field, as its name suggests, requires the two objects to be close, and probably touching. You might have a wireless charger for your smartphone, but you need to leave it sitting on the base in order for it to work. You can’t walk around the room and expect your device to charge in your pocket, or while you’re browsing Twitter next to the charger.
Far-field, or radiative wireless power, uses electromagnetic radiation -- in the form of microwaves or laser beams – directed at the device that needs to be powered. Problems arise with far-field wireless power because people generally need to stay out of the way of the electromagnetic fields, making it a less ideal solution for charging a device you carry in your pocket.
Wireless charging also requires both devices to have an antenna of sorts so that the antenna (or coil, or laser beam) in the base can transform the power into an electromagnetic field to send to a receiver, which then converts it back to electric power to charge the battery in your device.