Alpha: each subnet's own token
Besides TAO, every subnet has its own token, called alpha.
Each subnet has a pool that holds both TAO and that subnet's alpha. The pool sets the price between them. When more people want a subnet's alpha, its price in TAO goes up, and when fewer do, it goes down.
Alpha from one subnet is not the same as alpha from another. Each subnet's alpha has its own price, set by its own pool.
When you stake TAO into a subnet, it is swapped for that subnet's alpha at the pool's price. When you unstake, the alpha is swapped back into TAO. This is why the value of your stake can go up or down with the subnet.