Unconfirmed Transaction
An unconfirmed transaction is a broadcast transaction that has not yet been included in an accepted block according to the network's confirmation model.
✦ Key Insight
It matters because unconfirmed transactions can be delayed, replaced, dropped, or conflict with other spending attempts.
✕ Common Misconceptions
Broadcast does not guarantee confirmation, and different nodes can temporarily have different mempool views.
Detailed Explanation
In Practice
Dig Deeper
Confirmation
A confirmation indicates that a transaction has been included in a block and has gained additional blockchain history after it.
Mempool
A mempool is a node's temporary pool of valid, unconfirmed transactions waiting to be included in a block.
Transaction
A blockchain transaction is a signed or authorized instruction that changes blockchain state or transfers value when accepted by the network.
Network Fee
A network fee is the amount paid to have a blockchain transaction processed and included according to that network's fee rules.
Replace-by-Fee (RBF)
Replace-by-Fee is a Bitcoin mechanism that lets an unconfirmed transaction be replaced by a conflicting version that pays a higher fee.