Infrared is a very common type of wireless TV headphones. A type of electromagnetic energy, infrared, also known as IR is part of the same spectrum as x-rays, gamma rays, ultraviolet, radio waves, and microwaves. In a way, this makes infrared sound dangerous, but it's really not. In fact, visible light is also in this same spectrum. Infrared, derived from the Latin phrase "below red", is just that; a red light that is below what the human eye sees of the red color spectrum.
The fact that it is so close to visible light also highlights one infrared's main downfalls. In order to use an infrared device, you must remain within line of sight of the transmitter at all times. A good comparison would be to a television remote control. Notice that if you can't see the transmitter from where you're holding the remote, you get pretty much nothing at all. In the case of wireless TV headphone sets, this may or may not be a problem. Advances in technology that generally don't make it to cheaper items like remote controls have helped with the issue of line of sight, and although the same basic rules still apply, wireless headphones for TV use a bit of a broader spectrum which will cut down on some of the limitations. Also, in some cases, you can simply run the wire from the back of the television to a place on your entertainment center or television stand where you will have line of sight.
However, if this isn't possible, you'll want to look instead at RF or Bluetooth which, although possessing it's own downfalls, will at least travel through some solid objects though their range will be greatly diminished and, in the case of Bluetooth, likely destroyed unless we're talking about a thin entertainment center or bookshelf. To understand how infrared works, consider Morse Code, only with light instead of sound.
The various dots, dashes, and pauses are mutually known between transmitter and receiver, so when the transmitter sends a message, the receiver is able to decode it into plain English (or whatever). With infrared, there is something similar going on, only the transmitter is flashing lights at the receiver in a specific pattern that is mutually understood. We just can't see it because this light is just below the capability of our eyes. The receiver on the wireless TV headphone set then decodes these flashes into something that it can understand, which give it the information it needs to reproduce the sound coming from the transmitter.