HDMI over UTP/Cat6 is the first technology that allows you to send your HDMI signal long distances, un-compressed, over Cat5e / Cat6 Cable. This technology uses a special chipset that converts HDMI signal to one that can travel over Cat5e / Cat6 Cable and then convert it back to HDMI signal without any loss of quality. You see the same image as if you were just plugging in a short HDMI cable!
HDMI over UPT/Cat6 allows you to travel distances of approx. 50m-60m / 165ft-200ft over a single Cat5e / Cat6 cable and in some application pass IR signals as well.
The successor to HDMI over UTP/Cat6 is HDbaseT which allows you to go longer distances of upto 70m-100m / 228ft-328ft as well it has many other features like 4K resolutions, POE / POC (power over cable), Ethernet pass through, 2 Way IR, and USB pass through.
Although HDBaseT can go longer distances and has many other features, HDMI over UTP/Cat6 is still the most cost effective option for extending your HDMI signal when its distances are under 200ft and don't require any other features.