online
HUD
Also: heads-up display, tracking software
A heads-up display: software that overlays statistics about each opponent on the online table, drawn from a database of hands you have played against them. Many rooms now restrict or ban HUDs to protect recreational players.
Example. The HUD shows a player with 60% VPIP and 5% PFR — a passive calling station.
Typical HUD stats are VPIP, PFR, 3-bet percentage, fold-to-c-bet and aggression frequency. HUDs let regulars exploit specific opponents at scale, which is why sites such as GGPoker prohibit third-party tracking tools and instead provide their own built-in statistics.