Zero Confirmation Transactions, also known as "0-conf" or "unconfirmed transactions," refer to transactions on a blockchain network that have not yet been confirmed by the network's nodes. In a blockchain network, transactions are grouped into blocks and added to the blockchain through a process called mining. Until a transaction is confirmed and added to a block, it is considered unconfirmed or at "zero confirmation."

In some cases, merchants and exchanges may choose to accept zero confirmation transactions for smaller amounts or for transactions that are deemed to carry low risk. This is because a zero confirmation transaction is much faster than waiting for one or more confirmations, as the latter requires waiting for the transaction to be processed and added to a block. However, zero confirmation transactions are not considered to be as secure as transactions with one or more confirmations, as there is always a risk that the transaction could be reversed or double-spent.

Cryptocurrency exchanges: Some exchanges allow customers to trade cryptocurrencies before the transactions are confirmed, allowing for faster trades and a smoother user experience.

Point-of-Sale transactions: Some merchants accept zero confirmation transactions for small purchases, such as a cup of coffee or a quick snack, to reduce wait times for the customer and speed up the checkout process.

Online marketplaces: Online marketplaces, such as peer-to-peer marketplaces, may allow for zero confirmation transactions for low-value items or digital goods, as the risk of double-spending is deemed to be low for these types of transactions.

Let's say Alice wants to purchase a coffee from Bob's café using Bitcoin. Bob's café is set up to accept zero confirmation transactions for purchases under $10. Alice sends 0.05 BTC to Bob's café's wallet address and Bob immediately provides the coffee to Alice, even though the transaction has not yet been confirmed on the blockchain network. This is considered a zero confirmation transaction because it has not been confirmed by the network's nodes, but Bob has accepted the payment anyway because the transaction is deemed to carry low risk for small amounts like this.