One of around 20 different card games you can play online, H.O.R.S.E is a rotation of five mixed games - Hold'em, Omaha Hi Lo, Razz, Stud Hi and Stud Eight or Better (Stud Hi Lo).
Each game is played fixed limit for a round of 8 hands before switching. HORSE is played with max 8 players. Other variations include HEROS, to break up the Stud parts, HOSE to remove Razz, or RSE for a rotation of only Stud games.
The HORSE rotation starts with 8 hands of Limit Holdem.
Next up is 8 hands of Limit Omaha Hi/Lo, or LO8 for short.
The game then switches to Razz for another 8 hands.
The fourth game in HORSE is 7 Card Stud Hi.
Before repeating the rotation, a final 8 hands are played in 7 Card Stud Hi Lo.