Hearing aid & audiology glossary.

A

ACHIEVE trial

Aging and Cognitive Health Evaluation in Elders. A multicentre randomised controlled trial (Lin et al., Lancet 2023) testing whether a hearing intervention reduces 3-year cognitive decline in older adults with untreated hearing loss. Primary endpoint was null; a prespecified subgroup analysis suggested benefit in higher-risk older adults. See our full article on ACHIEVE.

Air-bone gap

The difference between air-conduction and bone-conduction thresholds on an audiogram at a given frequency. A meaningful gap (typically 10 dB or more) suggests a conductive component to hearing loss and warrants clinical evaluation rather than a consumer hearing aid.

Audiogram

A graph of hearing thresholds across frequencies (typically 250–8,000 Hz). Produced by pure-tone audiometry and used as the input to programming a hearing aid. The y-axis is hearing level in dB HL; the x-axis is frequency in Hz.

Audiologist

A licensed healthcare professional — typically holding a Doctor of Audiology (AuD) — who tests hearing, diagnoses non-medical hearing conditions, fits hearing aids, and programs cochlear implant processors. The point of care for any complex, asymmetric, or rapidly changing hearing loss.

Audiometry, pure-tone

The standard hearing test: tones at various pitches and volumes are played through calibrated headphones in a sound-treated booth, and the wearer indicates the softest tone they can detect at each frequency. The result is an audiogram. In-app hearing tests used by self-fitting hearing aids follow the same logic at lower precision.

B

Bone conduction

Hearing testing performed via a small vibrator placed on the mastoid bone behind the ear, bypassing the outer and middle ear and testing the inner ear directly. Plotted on audiograms as < (right ear) and > (left ear). The relationship between bone-conduction and air-conduction thresholds determines whether a hearing loss is sensorineural, conductive, or mixed.

BTE Behind-the-Ear

Hearing aid form factor in which the electronics sit behind the ear and a thin tube delivers sound to a dome in the ear canal. Durable, longer battery life, more visible than canal styles.

C

CIC Completely-in-Canal

Hearing aid that sits deep in the ear canal, nearly invisible from outside. Best for mild-to-moderate loss; small controls.

Cochlea

The spiral-shaped inner-ear organ that converts sound vibrations into nerve signals via thousands of sensory hair cells. Damage here causes sensorineural hearing loss.

Cochlear implant

A surgically implanted electronic device that stimulates the auditory nerve directly. Used for severe-to-profound sensorineural hearing loss. Not a hearing aid — covered by Original Medicare Part B when clinical criteria are met. See Does Medicare cover hearing aids?

Conductive hearing loss

Hearing loss caused by a problem in the outer or middle ear — earwax impaction, fluid, infection, eardrum damage, or ossicular issues. Often medically treatable; not appropriate for OTC hearing aids alone.

Configuration of hearing loss

The shape of an audiogram across frequencies. Common patterns: sloping (worse at higher frequencies, typical of age-related loss), ski-slope (abrupt high-frequency drop), flat, rising, cookie-bite (U-shaped), and notched (localized dip, often noise-induced). See how to read an audiogram.

Conversation Boost

Apple's directional focused-listening feature for AirPods Pro that prioritises sound from in front of the wearer. Used alongside the FDA-authorized Hearing Aid Feature.

D

dB HL decibel hearing level

Unit of hearing threshold relative to normal audiometric reference levels. Normal hearing is roughly 0–25 dB HL; mild loss 25–40; moderate 40–55; moderately severe 55–70; severe 70–90; profound 90+.

Directional microphone

A microphone configuration that prioritizes sound from in front of the wearer over sound from behind or to the sides. Critical for speech-in-noise performance in restaurants and crowds.

Dome (ear tip)

Soft silicone or foam tip that fits on the receiver of a RIC, BTE, or earbud-style hearing aid. Multiple sizes are typically included; fit is the single biggest predictor of daily wear.

E

ENT Otolaryngologist

Ear, Nose, and Throat physician (MD or DO). Appropriate point of care for sudden, one-sided, painful, or rapidly progressing hearing loss, or for any medical condition of the ear that may underlie hearing change.

F

FDA OTC Hearing Aid Final Rule

U.S. FDA rule published in the Federal Register on August 17, 2022 (87 FR 50698) and effective October 17, 2022, which created the regulated OTC hearing aid category for adults 18+ with perceived mild-to-moderate hearing loss. See the Federal Register notice.

Feedback (acoustic feedback)

Whistling caused by amplified sound leaking out of the ear canal and re-entering the microphone. Modern hearing aids use active feedback cancellation to suppress it.

FSA Flexible Spending Account

Employer-sponsored, pretax account for qualified medical expenses including hearing aids, hearing aid batteries, and hearing exams under IRS Publication 502. See how to reduce out-of-pocket cost.

G

Gain

The amount of amplification (in dB) a hearing aid adds at a given frequency. Programmed to match the wearer's audiogram.

H

Hearing Aid Feature HAF

Apple's FDA-authorized hearing aid software for AirPods Pro 2 and AirPods Pro 3, cleared via the De Novo pathway on September 12, 2024. The first OTC hearing aid software approved by the FDA. See Are AirPods Pro hearing aids?

HSA Health Savings Account

Tax-advantaged account paired with a high-deductible health plan, used for qualified medical expenses including hearing aids, batteries, and hearing exams under IRS Publication 502.

I

ITC In-the-Canal

Hearing aid that sits partially in the ear canal. Less visible than ITE; smaller battery.

ITE In-the-Ear

Custom-molded hearing aid that fills the bowl of the outer ear. Larger than canal styles; easier to handle for adults with dexterity limitations.

L

Lancet standing Commission on dementia

International expert panel convened by The Lancet to synthesise evidence on modifiable risk factors for dementia. The 2024 report (Livingston et al.) identifies hearing loss as one of the largest modifiable midlife risk factors in its population-attributable-fraction framework. See our explainer.

M

Masking (audiometric)

Adding noise to the non-test ear during a hearing test so that ear does not detect the tone intended for the test ear. Masked thresholds are plotted with triangle (right) and square (left) symbols.

Medicare Advantage Part C

Private insurance plans that provide all Original Medicare benefits and typically add benefits Original Medicare excludes. Approximately 97% of Medicare Advantage plans in 2026 offer some hearing benefit, often $500–$2,500+ per ear toward hearing aids. See Does Medicare cover hearing aids?

Medigap Medicare Supplement Insurance

Private supplemental insurance that covers cost-sharing (deductibles, copays, coinsurance) on services Original Medicare already covers. Does not cover hearing aids, because Original Medicare does not.

Mixed hearing loss

Hearing loss with both conductive and sensorineural components. Requires medical evaluation alongside any hearing aid fitting.

O

Occlusion

The plugged-up sensation that can occur when an ear canal is sealed by a hearing aid dome or earbud tip, often more noticeable with one's own voice. Vented hearing aids reduce the effect; tightly-sealing earbuds (including AirPods Pro) can amplify it.

OTC hearing aid Over-the-Counter

FDA-regulated medical device sold directly to adults 18+ with perceived mild-to-moderate hearing loss without a clinic visit, prescription, or fitting by a licensed professional. Established by the FDA Final Rule effective October 17, 2022.

Ototoxic

Damaging to the ear, particularly the inner ear or auditory nerve. Some medications — certain chemotherapy agents, aminoglycoside antibiotics, high-dose loop diuretics — are ototoxic. Hearing loss after recent ototoxic medication exposure warrants clinical evaluation.

P

Presbycusis age-related hearing loss

Gradual sensorineural hearing loss associated with aging, usually beginning in the higher frequencies. About 1 in 3 U.S. adults aged 65–74 has hearing loss per the NIDCD, and nearly half of those 75 and older.

Prescription hearing aid

Hearing aid dispensed by a licensed audiologist or hearing-aid specialist after a clinical fitting. Required for severe and profound hearing loss and for all pediatric cases. See OTC vs Prescription Hearing Aids.

PSAP Personal Sound Amplification Product

Unregulated consumer-electronics product that amplifies ambient sound. Not an FDA-regulated medical device. Not designed for hearing loss. Distinct from an OTC hearing aid.

Pulsatile tinnitus

Tinnitus that pulses in time with the heartbeat. May indicate a vascular cause such as turbulent blood flow near the ear and warrants medical evaluation rather than a consumer hearing aid trial. See our tinnitus evidence review.

R

Real-ear measurement REM

A probe-microphone measurement made inside the ear canal that verifies what a hearing aid is actually delivering to the eardrum. Considered best-practice verification for prescription fittings.

RIC Receiver-in-Canal

Hearing aid form factor similar to BTE but with the speaker (receiver) sitting in the ear canal rather than behind the ear. Common in modern prescription and self-fitting OTC devices.

S

Self-fitting hearing aid

FDA-recognized subcategory of OTC hearing aid that calibrates itself to the wearer via an in-app hearing test rather than a clinician's fitting software. See How self-fitting hearing aids work.

Sensorineural hearing loss

Hearing loss caused by damage to the inner ear or auditory nerve. Usually permanent. The type of loss hearing aids are designed to compensate for.

Sound therapy

The use of low-level shaped noise — through a sound generator, a hearing aid program, or a mobile app — to reduce the perceived intrusiveness of tinnitus. Listed as an option in the AAO-HNS Tinnitus Clinical Practice Guideline.

Speech-in-noise SIN

The ability to understand speech in the presence of background noise (restaurants, parties, multi-talker rooms). The most common practical complaint among adults with age-related hearing loss, and the most important real-world target for a hearing aid.

T

Telecoil T-coil

A small copper coil inside some hearing aids that picks up the magnetic signal from hearing-loop systems in theaters, places of worship, and transit hubs. Improves clarity in looped venues.

Tinnitus

The perception of ringing, buzzing, hissing, or other sounds in the ears without an external source. Often accompanies hearing loss. Persistent or one-sided tinnitus warrants evaluation by a clinician.

Tympanic membrane eardrum

The thin membrane that separates the outer ear from the middle ear and transmits sound vibrations to the ossicles (the three small middle-ear bones). Damage to the eardrum can cause conductive hearing loss.

V

Vestibular schwannoma acoustic neuroma

A benign, slow-growing tumour on the vestibulocochlear nerve. Often presents with one-sided hearing loss, one-sided tinnitus, or balance change. A reason for prompt ENT evaluation, not addressable with a consumer hearing aid.