Noun
sidetone (countable and uncountable, plural sidetones)
The effect of sound that is picked up by the telephone's mouthpiece and introduced (at low level) into the earpiece of the same handset, acting as feedback; or a similar effect in radiotelegraphy, public-address systems, etc.
Aside from improved call quality (they have a sidetone feature), the Momentum True Wireless 2 have the same stellar sound -- for true wireless earbuds, anyway -- offering clearly superior sound quality to the AirPods Pro. Source: Internet
I never feel all that confident using true wireless earphones for phone calls as the absence of sidetone makes me speak a little louder than I should. Source: Internet