Wireless, in this context, means that your hearing aids have a feature that creates a direct wireless connection to media sound sources like your television, stereo, computer or phone. With wireless, you get the sound you want to hear streamed right into your ears at the volume most comfortable for you. Other people in the room use the television remote control to set the volume they prefer. There are several types of wireless technology available in hearing aids today:

Near-field magnetic induction (NFMI) systems use Bluetooth® technology to stream audio from the transmitting device to an intermediary relay device worn around your neck, which in turn transmits to your hearing aids. NFMI was the first wireless technology; the transmission range is limited to 3-5 feet and there can be a sound delay with the device.
900 MHz Radio-Frequency (RF) systems use an antenna to transmit to your hearing aids. You plug a small transmitting device into your television's "audio out" jack; the transmitter streams the audio directly to your hearing aids. The range is greater than with NFMI systems – about 20-30 feet from the television or stereo. RF systems do not require a relay device worn around your neck. RF systems on the 900 MHz band support long-distance audio streaming as well as reliable communication between both hearing aids for binaural, or ear-to-ear, processing. In effect, your hearing aids are able to share information with each other to improve sound management in many situations. The transmission device can stream audio to more than one hearing aid wearer at a time.

2.4 GHz band Radio-Frequency systems transmit on the 2.4 GHz band, a frequency commonly used by many home electronics such as computer networks, garage door openers and wireless phones. These systems also support long-distance audio streaming, although there is some debate about whether users experience interference from the household devices mentioned above. The 2.4 GHz platform does not support ear-to-ear processing.
An FM system is used with hearing aids or stand-alone to give additional assistance in difficult listening situations such as in background noise, when trying to listen at too much distance from the source of sound or in a reverberant (echo-prone) hall or room. The receiver part may be incorporated into the hearing aid, or attached by a cable, or worn around the neck like a hearing loop. The transmitter part is held by the person speaking or close to the sound that you wish to pick up – eg plugged into a TV socket or audio device. When someone speaks into the transmitter’s microphone, the voice is transmitted by radio waves without interference from other noise. FM thus helps understanding in noisy situations.