Tie ratio. Do you know what that means? It's the number of games purchased divided by the number of consoles sold. In the case of Wii U, Gamestop is reporting 1.2 million games pre-ordered and 500,000 consoles pre-ordered.
1.2 million divided by 500,000 gives us 2.4. This number is a handy metric, because it expresses on average, the number of games any given console owner is going to buy over the course of the console's lifetime. So at launch, at Gamestop, the Wii U's launch tie ratio is 2.4, but that number could increase or decrease over time.