A bin is simply a container in which liquidity is held within a pool at a fixed price point. It can contain one of the tokens or both or none at all. But only the active bin can contain both tokens.
As swaps go through the pool, the tokens are swapped one for the other within this bin. Once all of one token is converted to the other, the price moves to the next bin.
As long as the swaps stay within the same bin, there is zero slippage for the swap, which makes it more attractive for the swapper.
In this example we see our own liquidity distributed across 7 bins. Below it in grey is a representation of all liquidity within that bin from all liquidity providers, including yours.
Once a bin is created, it cannot be moved or destroyed, it exists on the blockchain forever and can be used by anyone at any time.