First of all HUD is short for Heads Up Display. For most of us we encounter HUDs in gaming. The HUD will show things like how much life your character has, how your armor is doing. Maybe, the HUD will indicate your current selected tool/weapon, how much ammo you have, are you taking damage. And, in some games the HUD will even indicate the map direction you are going, etc. Basically it is a compendium of useful information that you might need to navigate the video game.
In the case of Urthgame Orbs, the HUD has additional functions that can be much more important than just showing you a snapshot of your current stats situation.
Once you have developed some facility at splitting your attention between the Orb environment and the HUD, you will be able to navigate the Orb and at the same time have a portion of your attention on the HUD.
This means that when you open a chest, or touch an object, or accomplish a specific goal you can observe and hopefully notice the effect that this has on the attributes in the HUD. This allows you to create a secondary overlay map of the Orb.
In addition to a “map” that contains information such as where the doors and rooms and hallways are, you can create a map that designates active elements. For example, over here is a table that when I encounter it will give me a textual read out and increase my “Luck”.
As you run the Orb with this split attention a new dimension (or dimensions) will reveal itself. You will see certain areas and events that appear to be the same from run to run and from person to person. You will see other areas and events that change depending upon the run and depending upon the person you are running for. And, sometimes you will notice an area or event that you thought was constant suddenly give you a different reading on the HUD.
All of this comes from being able to notice real time the change in the HUD in addition to being able to read the cumulative attribute levels.
I hope this gives you a useful perspective.