Alternative phrasing for an unconfirmed transaction.
Every transaction must be included in a block in order to be acknowledged by the network as a valid transfer of funds.
After a transaction is sent, it enters one of three states: Unconfirmed pending confirmation, confirmed or rejected.
Confirmation may be delayed if the transaction fee is not high enough for the miners who validate transactions or if there is a high volume of transactions waiting to be processed. Zero confirmation transactions are also known as unconfirmed transactions.