HUD is an abbreviation of Heads-Up Display which usually means variety of user interfaces. In Hand2Note by word HUD we mean stats displayed on each player right over the table.
Hand2Note supports 3 types of Poker HUD: Static HUD, Positional HUD and Dynamic HUD.
Static HUD shows the same stats for all players at the table. You probably used this kind of HUD in other software.
Positional HUD shows different stats for different players at the table depending on their positions, hero's position, stacksizes, number of players in hand and many other criteria known on the beginning of a hand.
Dynamic HUD shows stats depending on players' actions in hand. For example, it may show stat OPEN RAISE MP only when player open raises from middle position.
Figure 1. Positional HUD example in Hand2Note
Positional and dynamic HUDs are prohibited on PokerStars, but allowed in other rooms.