Usually when you see a set of three numbers varying between 1 and 2 next to a battle pet in a guide or write-up, it's usually indicating which abilities to pick/use for a specific strategy.
1 = default ability in the slot
2 = second ability in the same slot (second choice in the drop-down option)
Example: Orange Tabby Cat
Slot 1 = 2, which would be Pounce (Claw being 1, aka the default option)
Slot 2 = 2, which would be Screech
Slot 3 = 1, which would be Devour
In what context are you seeing these numbers? The above may not always apply, but it's hard to say without knowing how the information is being displayed.