Audio Frequency Induction Loop Systems (A.F.I.L.S) are used by hearing aid wearers to assist them to hear clearly in difficult acoustic environments e.g. churches, theatres, reception areas, etc.
Induction loops replace the sound path between the signal sound and the hearing aid wearer with a magnetic field. The magnetic field is induced into the ‘telecoil’ (hence the ‘T’ programme) which is featured on most hearing aids, and converted back to audio. When a hearing aid is switched to the ‘T’ programme the microphone on the hearing aid is (normally) disconnected, so the user simply hears what is fed into the induction loop system, without the background noise.
Definition from soundinduction.co.uk.