As I remember from many years ago a "balun" was a device used in RF systems usually to match an input or output to coax. It was usually a transformer but could have been resistive also.
In this industry the device used to match or convert an unbalanced input or output to balanced and vice versa was always called by what it actually was- transformer, active converter, matching pad, etc.
It seems that now a "balun" is something that allows you to use CAT5 for something that it was not intended. It could be anything from a keystone wallplate insert with an RCA jack that connects directly to the cable to converters that extend HDMI distances. Unfortunately CAT5 has become the universal cable that gets used for everything from doorbells to video.
I can't wait for the day that the computer industry does away with UTP and adopts fiber. CAT5 will become a thing of the past and then what will people do? I hope use the proper cable or fiber.
-Hal