First of all, what the heck is a mempool.

A mempool (memory+pool) is a crypto node's mechanism for storing information on unconfirmed transactions.

Kinda like a waiting room for transactions before they're included in a block.

Sui's mempool is called 'Narwhal' and it's designed to improve the efficiency when it comes to sharing transactions in the mempool among validators in a blockchain network.

Mempools are usually local to each validator, which means the data included needs to be shared and verified before being included in a block.

With Narwhal, instead of including transaction data in the consensus process like traditional blockchains, the mempool is handled independently and base the consensus on metadata (block headers and hashes).

Put simply, the consensus and the mempool can do their respective job(s) individually, without having to worry about one another.