For tagging purposes: Small speakers with a hook design meant to be held by the ears, they have no headband (ala headphones). This also includes earbuds, which are placed over the ear canal and also requires no headband, this type of device is popular with digital media players like the iPod.
Images where a character's ears are covered up, but there are visible earphone cable leading to them and no visible headphone band present can also be tagged earphones.
Misc: The actual definition of an earphone is a device that converts electrical energy into sound waves and is worn over or inserted into the ear, thus earbuds, headphones, and headsets would all be considered types of earphones.
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