Y-jack

plural Y-jacks

1. A splitter; a device used to split a single jack into two.

   If you bring along your own pair of headphones and a Y-jack, two people can share one audioguide and save.

   2007, Rick Steves, Pat O'Connor, Rick Steves' Ireland 2008, page 14

   1 more example

   The answer is a small, inexpensive, plastic doodad called a splitter (or Y-jack), which as its name suggests splits a single phone jack into two. So now you can plug your computer and phone into the same wall jack

   2006, Edward C. Baig, Macs For Dummies, 9th edition, page 137

   Synonyms: Y-splitter