HUD stands for Heads Up Display, and refers to software that compiles statistics on players’ hand histories. Using a HUD means you can get real-time data on opponents’ poker styles even as you play against them. You’ll learn whether they tend to raise before the flop, how aggressive they are, and so on. HUDs have been banned by some sites, so it’s important to check the specific policy of your chosen site if you’re hoping to use third-party apps like HUDs.