Pending is the status of a payment or transaction that has been sent but not yet confirmed by the network or the payment system. The funds are, as it were, stuck in an intermediate state and awaiting a final decision.

A confirmation is the inclusion of a transaction in a block of the blockchain and the fixing of its validity. The more confirmations a transfer gathers, the more reliably it is considered irreversible.

A transaction fee is the payment the sender of a transfer pays the network for processing and confirming the operation. Its amount depends on the network load and the priority of the transfer.

An output is the part of a Bitcoin transaction that sets the recipient's address and the transfer amount. A single transaction can have several outputs at once: for different recipients and to return change to the sender.

Double spending is an attempt to spend the same coins twice. This is a key problem of digital money, which the blockchain solves using a distributed ledger and transaction confirmations.