This cable comes from Choseal, 3.5mm (1/8") stereo jack splitter cable.
This 5ft long cable has a stereo 3.5mm male plug (the kind that plugs into an iPod, MP3 player, computer etc.) 
on one end, and two stereo female 3.5mm jacks on the other end. This cable will allow you to plug two sets of stereo headphones into one jack. 

Specification: 
A stereo 3.5mm male plug connector and two stereo female 3.5mm jacks on the other end 
You can plug two sets of stereo headphones into one jack 
Easy to use such as: Walkman, portable CD/DVD player, MP3 player, computer etc.