Confirmation time is defined as the time elapsed between the moment a blockchain transaction is submitted to the network and the time it is finally recorded into a confirmed block. In other words, it represents the total time a user has to wait until their transaction gets collected and confirmed by a miner node.
Depending on the type of blockchain and network architecture, this time can be reduced by offering a higher transaction fee, so miners will have an incentive to give a higher priority to your transaction.
Confirmation time can be used as a metric to measure the average speed of a blockchain network. However, since the actual time between submission and confirmation can vary due to individual factors and fluctuating demand, it is more reasonable to calculate the efficiency and speed of a blockchain by making use of an averaged confirmation time according to its current state and the most recent blocks.
After a transaction has been included in a block by a miner, the block needs to be validated by the other nodes of the network. When the block is confirmed to be valid, the transaction is considered to have a single confirmation, meaning that each new block that is mined on top of that will represent another confirmation.
As the most recent blocks in a blockchain are not considered as fully secure, it is often recommended to wait for additional block confirmations before considering the transaction successful and irreversible. This is especially true for the parties that are receiving cryptocurrency payments, such as merchants and online service providers.