A blockchain transaction that has been broadcast to the network but has not yet been included in a validated block by miners or validators. Unconfirmed transactions sit in the mempool waiting to be picked up, and their processing time depends on network congestion, the fee attached, and the blockchain's block time. Most exchanges and services require multiple confirmations before considering a transaction finalised to reduce the risk of double-spending.
Example
“The Bitcoin transfer showed as unconfirmed for over two hours because the sender attached a low transaction fee during a period of high network congestion.”