The phrase "headphone socket" refers to a small hole or opening on a device where you can plug in your headphones, allowing you to listen to audio privately without disturbing others. Full definition
There's a standard 3.5 mm headphone socket on top, where you'll also find a small power switch and volume rocker is to be found on the phone's right side. (pocket-lint.com)
In terms of connections, you'll find a 3.5 mm headphone socket on the top alongside the power / standby button. (pocket-lint.com)
Both also cast off the 3.5 mm headphone socket in the process. (pocket-lint.com)