The default channel is the channel that is preset, also known as the start up channel.
Receivers attach to the hearing aids via the audio shoe. They receive the FM signal from the transmitter and relay the speaker's voice directly to the student's hearing aids.
The transmitter is the device that transmits the signal to the receivers. It has a small microphone (usually in the form of a lapel mic, which attaches to the users clothing, or a boom mic or headset). The users speech signal is transmitted via FM directly to the student's FM receivers.
Audio shoes are special connectors that enable the student's hearing aid to accommodate the receivers (they are specific to the student's make/model of hearing aids).
Synchronizing is matching the channel of the receivers to the transmitter. (It is necessary to synchronize students receivers with the transmitter when students from different classes are working together and need to listen to instructions from one teacher.)
Interference is the undesired noise picked up by FM receivers due to a source external to the FM system.