Informal name for a portion of a transaction output that is returned to the sender as a “change” after spending that output. Since transaction outputs cannot be partially spent, one can spend 1 BTC out of 3 BTC output only by creating two new outputs: a “payment” output with one BTC sent to a payee address, and a “change” output with remaining 2 BTC (less transaction fees) sent to the payer’s addresses. BitcoinQT always uses new an address from a key pool for enhanced privacy. Blockchain.info sends to a default address in the wallet. A common mistake when working with a paper wallet or a brain wallet is to make a change transaction to a different address and then accidentally delete it. For example, when importing a private key in a temporary BitcoinQT wallet, making a transaction and then deleting the temporary wallet which contains the change.
Malone, J.A (2015). Glossary of Bitcoin Terms and Definitions. United States: Lulu Press, Inc