Mempool
The waiting area where valid transactions sit until a miner or validator includes them in a block.
The mempool (memory pool) is the set of transactions that nodes have received and checked but that are not yet in a block. Every node keeps its own copy, so there is no single mempool, but they usually look similar.
On Bitcoin and similar chains, block space is limited, so miners pick the transactions that pay the highest fee per unit of size. When the mempool is crowded, low-fee transactions can wait for hours or, in extreme cases, be dropped. Mempool explorers show current fee levels, which helps you choose a fee that confirms in reasonable time.
For swaps, a stuck deposit is often simply a transaction waiting in the mempool. If your wallet supports Replace-by-Fee or Child-Pays-for-Parent, you can speed it up by paying more. Otherwise, the transaction confirms once demand drops.
