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

Typically used to connect an audio device to your computer.
Every computer sound card I've seen has a 3.5mm socket for audio input.
Many portable audio devices(MP3 players, CD players etc) have 3.5mm sockets, usually used for headphones/earphones.

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)