Adjective
open-back (comparative more open-back, superlative most open-back)
Of headphones: only partially covering the ear, so that there is airflow to the wearer's ears.
Synonyms: open-ear, open-eared
Antonym: closed-back
Although I have mixed feelings about semi-open headphones, they can be great for someone who wants a more spacious sound and lively imaging without having to worry about leakage that open-back headphones emit. Source: Internet
Open-back and resonator Some banjos have a separate resonator plate on the back of the pot to project the sound forward and give the instrument more volume. Source: Internet
Open-back banjos generally have a mellower tone and weigh less than resonator banjos. Source: Internet
In fact, when I compared the Wave 5 to Oppo’s open-back PM-2 planar magnetic headphone, the Oppo PM-2 delivered a more relaxed and spacious musical presentation. Source: Internet