耳机 (ěr jī) literally means 'ear machine' — 耳 (ěr) means 'ear', and 机 (jī) means 'machine' or 'device'. Together, they refer to a pair of small audio devices worn over or in the ears to listen to sound privately. Unlike speakers, headphones deliver sound directly to the listener without disturbing others, making them essential for commuting, studying, working remotely, or enjoying music quietly.

This word is neutral in register and used widely across spoken and written Chinese. It applies to all common types: wired earbuds, over-ear headphones, and wireless Bluetooth models. While 耳机 is the standard term, context may specify type — e.g., 蓝牙耳机 (lán yá ěr jī) for 'Bluetooth headphones' or 入耳式耳机 (rù ěr shì ěr jī) for 'in-ear headphones'. The compound follows the common Chinese pattern of noun + device classifier, emphasizing function over form.