In hi/lo split poker games such as Omaha Hi/Lo or Stud Hi/Lo, a hand consisting of the ace, two, three, four, and five of the same suit. It is simultaneously the best possible low hand (5-4-3-2-A) and a very strong high hand (straight flush), and will therefore almost always win at least 3/4 of the pot. Wheel
refers to any 5 high straight, the flush is what makes it a "steel" wheel.
Last time I got quads playing Omaha on Pokerstars, someone had a steel wheel and he ended up scooping the pot.