Brand new extension cable = 3.5mm plug to 3.5mm socket, stereo audio.
Cable length: 2 metres

Ideal for using headphone/earphones at a more comfortable distance, or for connecting devices that aren't close together.

Examples of devices that use 3.5mm audio plugs:
MP3 players
Portable CD/DVD players
Walkmans(portable cassette player)
Every computer sound card I've seen has a 3.5mm socket for audio output & input.

Can also be used for any other audio devices that have standard 3.5mm audio sockets of course.
This excludes some minidisc player/recorder sockets, as some have a special 3.5mm socket that actually uses an optical signal(light shines through cable)