A dual headphone adapter is a device that allows two headphones to be connected through to one audio jack. They are quite useful when wanting to share music with friends, such as on an MP3 player, CD player, or boombox. Although earbuds, a type of headphone design, can be shared with a friend (with one bud in another's ear), a dual headphone adapter can be more practical. They can purchased at various audio/visual and electronic stores, such as RadioShack, for as little as $5 USD.