Apple has two naming schemes for their operating system: numbers (10.4, 10.5, and so on), and types of animals (Tiger, Leopard, and so on). They use these inconsistently in their marketing. I know the number I am using (10.5), but I always forget which animal this is represented by. And they don't tell me when I ask:
I hope the next version of the OS will at least let me find out what animal I am dealing with. Given that they are planning to call it "Snow Leopard", the confusion will be huge, so making this easy to find will be important.