Classic, decentralized cryptocurrencies wait a while until enough blocks are confirmed. This prevents a transaction from being reversible. Thus, there can be no double spending (double-donation), in which an amount is used twice. This process is time-consuming and may take different amounts of time depending on the blockchain, with the block times involved, until the 6 generally accepted blocks have been acknowledged. Other cryptocurrencies allow faster confirmation times by having a centralized authority with some degree of control over the network.
Projects that have integrated a second network level, the so-called Masternodes, in their blockchain can overcome these two problems. Master nodes can be invoked in a quorum confirming that a transaction is valid. If it is valid, the master nodes "lock" the inputs of the transaction and pass this information to the network. This ensures that the transaction is entered in the next block. This also guarantees that the same inputs will not be used a second time while the receiver is waiting for confirmation.
Cryptocurrencies, such as Dash, can compete with instant transaction systems such as credit cards using InstantSend technology without relying on one central authority. Widespread use of Dash and InstantSend could revolutionize the world of cryptocurrencies, allowing them to reduce long one-hour verification times (like Bitcoin) to a few seconds.
Most of this information was acquired and generalized by Dash Core, for the most part.