The Shared Piggy Bank
On a stock exchange you wait for a seller. On Solana's AMMs there is no order book and nobody to wait for. You trade against a shared pot of tokens that anyone can fill and anyone can draw from.
Simply put, a liquidity pool is a wallet the market owns. It holds two tokens - here SOL and fUSDC - and it prices every trade off the ratio sitting between them.
The pot obeys one rule:
x · y = k
x is the SOL inside, y is the fUSDC inside, and k is the product of the two. A swap is not allowed to change k. You cannot empty the pot, because pushing SOL out forces y upward, which makes every remaining SOL more expensive.
Depth is what decides how much that costs you. The pool you will trade in the simulator holds about $4,000. The deep pool holds about $400,000. Same $50 order in both. One is a visible fraction of the shallow pot; the other is dust. That self-inflicted price move is , and it is the most common way a swap quietly returns less than you expected.