In poker, the term HUD is actually an abbreviation for “Heads Up Display,” which is a piece of software that shows some of the important statistical information about players.
When running a HUD, a player will have information about his opponents’ willingness to enter pots (VPIP), how often they raise first (RFI), their 3-bet tendencies, and other poker stats.
A HUD has been an essential part of an online player’s arsenal for many years, but these days, more and more rooms are banning outside HUDs for tracking hand histories, replacing them with their own, or removing them altogether.