noun. A small speaker that is worn over or in the ear, often as one of a pair connected by a wire attached to a band running over the head

noun. A listening device placed or worn in the ear, usually sold in pairs

noun. electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear

"Razer has moved to an open-back, ear-encompassing headphone, which is good for those of us who don't like stuff actually sitting on our ears, and I personally think it helps with sound placement as well."

electro-acoustic transducer  

earplug  receiver  telephone receiver  

Bluetooth  Ethernet  adapters  adaptor  amplifier  

acoustical network  capacitor speaker  coaxial speaker  cone  crossover network