Headphones are a hardware device that can be plugged into a computer, laptop, smartphone, mp3 player or other device to privately listen to audio without disturbing anyone in the vicinity. They are plug-and-play devices and do not require any sort of installation before use.
Headphones originally consisted of one speaker for each ear, connected by a band over the head. While this style is still in use, modern headphones are also available in a much smaller format that is inserted into the ear, and commonly called ear buds. Modern-day headphones can be either wireless or wired.
These are designed in contrast to loudspeakers that produce sound that can be heard by anyone in the area.